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VALVES TRAINING BOOK (2008)

BY : ENG. ALY FARAG (EX. CHAIRMAN ASSISTANT OF P.P.CO.)

REVIEWED BY:

ENG. HANY DAHY ( CHAIRMAN OF PETROJET CO.)

ENG. SADEK HEFZY ( CHAIRMAN OF EGYPT MAINT. CO.)

اللهم اجعل هذا العلم صدقة جاريه لروح من أعده (2)

Introduction: A valve is a mechanical device that controls the flow of fluid and pressure within a system or process. A valve controls system or process fluid flow and pressure by performing any of the following functions:

Stopping and starting fluid flow.

Varying (throttling) the amount of fluid flow.

Controlling the direction of fluid flow.

Regulating downstream system or process pressure.

Relieving component or piping over pressure. There are many valve designs and types that satisfy one or more of the functions identified above. A multitude of valve types and designs safely accommodate a wide variety of industrial applications. Regardless of type, all valves have the following basic parts: the body, bonnet, trim (internal elements), actuator, and packing. The basic parts of a valve are illustrated in Figure 1.

1- VALVES:

(1-1) VALVE BASIC PARTS: (1-1-1) Valve Body: The body, sometimes called the shell, is the primary pressure boundary of a valve. It serves as the principal element of a valve assembly because it is the framework that holds everything together. The body, the first pressure boundary of a valve, resists fluid pressure loads from connecting piping. It receives inlet and outlet piping through threaded, bolted, or welded joints. Valve bodies are cast or forged into a variety of shapes. Although a sphere or a cylinder would theoretically be the most economical shape to resist fluid pressure when a valve is open, there are many other considerations.

(3) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

For example, many valves require a partition across the valve body to support the seat opening, which is the throttling orifice.

Figure 1 : Basic Parts of a Valve With the valve closed, loading on the body is difficult to determine. The valve end connections also distort loads on a simple sphere and more complicated shapes. Ease of manufacture, assembly, and costs are additional important considerations. Hence, the basic form of a valve body typically is not spherical, but ranges from simple block shapes to highly


complex shapes in which bonnet is a removable piece to make assembly possible, forms part of the pressure resisting body. Narrowing of the fluid passage (venturi effect) is also a common method for reducing the overall size and cost of a valve. In other instances, large ends are added to the valve for connection into a larger line.

(1-1-2) Valve Bonnet: The cover for the opening in the valve body is the bonnet. In some designs, the body itself is split into two sections that are bolted together. Like valve bodies, bonnets vary in design. Some bonnets function simply as valve covers, while others support valve internals and accessories such as the stem, disk, and actuator. The bonnet is the second principal pressure boundary of a valve. It is cast or forged of the same material as the body and is connected to the body by a threaded, bolted, or welded joint. In all cases, the attachment of the bonnet to the body is considered a pressure boundary. This means that the weld joint or bolts that connect the bonnet to the body are pressure-retaining parts. Valve bonnets, although a necessity for most valves, represent a cause for concern. Bonnets can complicate the manufacture of valves, increase valve size, represent a significant cost portion of valve cost, and are a source for potential leakage.

(1-1-3) Valve Trim: The internal elements of a valve are collectively referred to as a valve's trim. The trim typically includes a disk, seat, stem, and sleeves needed to guide the stem. A valve's performance is determined by the disk and seat interface and the relation of the disk position to the seat. Because of the trim, basic motions and flow control are possible. In rotational motion trim designs, the disk slides closely past the seat to produce a change in flow opening. In linear motion trim designs, the disk lifts away from the seat so that an annular orifice appears.


(1-1-4) Disk and Seat: For a valve having a bonnet, the disk is the third primary principal pressure boundary. The disk provides the capability for permitting and prohibiting fluid flow. With the disk closed, full system pressure is applied across the disk if the outlet side is depressurized. For this reason, the disk is a pressure-retaining part. Disks are typically forged and, in some designs, hard-surfaced to provide good wear characteristics. A fine surface finish of the seating area of a disk is necessary for good sealing when the valve is closed. Most valves are named, in part, according to the design of their disks. The seat or seal rings provide the seating surface for the disk. In some designs, the body is machined to serve as the seating surface and seal rings are not used. In other designs, forged seal rings are threaded or welded to the body to provide the seating surface. To improve the wear-resistance of the seal rings, the surface is often hard-faced by welding and then machining the contact surface of the seal ring. A fine surface finish of the seating area is necessary for good sealing when the valve is closed. Seal rings are not usually considered pressure boundary parts because the body has sufficient wall thickness to withstand design pressure without relying upon the thickness of the seal rings.

(1-1-5)Stem: The stem, which connects the actuator and disk, is responsible for positioning the disk. Stems are typically forged and connected to the disk by threaded or welded joints. For valve designs requiring stem packing or sealing to prevent leakage, a fine surface finish of the stem in the area of the seal is necessary. Typically, a stem is not considered a pressure boundary part. Connection of the disk to the stem can allow some rotation to


ease the positioning of the disk on the seat. Alternately, the stem may be flexible enough to let the disk position itself against the seat. However, constant fluttering or rotation of a flexible or loosely connected disk can destroy the disk or its connection to the stem. Two types of valve stems are rising stems and nonrising stems. Illustrated in Figures 2 and 3, these two types of stems are easily distinguished by observation. For a rising stem valve, the stem will rise above the actuator as the valve is opened. This occurs because the stem is threaded and mated with the bushing threads of a yoke that is an integral part of, or is mounted to, the bonnet.

Figure 2 Rising Stems

There is no upward stem movement from outside the valve for a nonrising stem design. For the nonrising stem design, the valve disk is threaded internally and mates with the stem threads.


Figure 3 : Nonrising Stems

(1-1-6) Valve Actuator: The actuator operates the stem and disk assembly. An actuator may be a manually operated handwheel, manual lever, motor operator, solenoid operator, pneumatic operator, or hydraulic ram. In some designs, the actuator is supported by the bonnet. In other designs, a yoke mounted to the bonnet supports the actuator. Except for certain hydraulically controlled valves, actuators are outside of the pressure boundary. Yokes, when used, are always outside of the pressure boundary.

(1-1-7) Valve Packing: Most valves use some form of packing to prevent leakage from the space between the stem and the bonnet. Packing is commonly a fibrous material (such as flax) or another compound (such as teflon) that forms a seal between the internal parts of a valve and the outside where the stem extends through the body.


Valve packing must be properly compressed to prevent fluid loss and damage to the valve's stem. If a valve's packing is too loose, the valve will leak, which is a safety hazard. If the packing is too tight, it will impair the movement and possibly damage the stem.

(1-2) Valves Classification: Introduction: Because of the diversity of the types of systems, fluids, and environments in which valves must operate, a vast array of valve types have been developed and may be classified as it is shown in the following figure.

(1-2-1)Classification Based on Mechanical Motion : Based on the mechanical or cyclical motion of the valve closure

member, valves are classified as follows:


(1-2-1-1)Linear Motion Valves :

The valves in which the closure member, as in gate, globe,

diaphragm, pinch and lift check valves, moves in a straight line

to allow, stop, or throttle the flow. Table (1) lists the valves

based on motion of valve-closure member.

TABLE (1) Classification of Valves Based on Motion

Valve type Linear motion Rotary motion Quarter turn

Gate valve X

Globe valve X

Swing check valve X

Lift check valve X

Tilting-disc check valve X

Folding-disc check valve X

In-line check valve X

Stop check valve X X

Ball valve X X

Pinch valve X

Butterfly valve X X

Plug valve X X

Diaphragm valve X

Safety valve X

Relief valve X

Notes: Tilting-disc check valves are in the same category as swing check valves in regard to motion of the disc. When a swing check valve is provided with the external means to close and maintain the valve disc in a closed position, it can be used as a stop check valve.

صدقة جاريه لروح من أعدهاللهم اجعل هذا العلم (10)

(1-2-1-2) Rotary Motion Valves :

When the valve-closure member travels along an angular or

circular path, as in butterfly, ball, plug, eccentric and swing

check valves, the valves are called rotary motion valves.

SeeTable (1).

(1-2-1-3) Quarter Turn Valves :

Some rotary motion valves require approximately a quarter

turn, 0 through 90°, motion of the stem to go to fully open

from a fully closed position or vice versa. Refer to Table (1).

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(1-2-2) Classification Based on valve size:

Valve size is denoted by the nominal size of the pipe flange on

which the valve is connected. There are two types of this

classification.

(1-2-2-1) Small valves:

They are valves whose diameters are equal or smaller than a

Nominal Pipe Size (NPS = 2 in.) In US system or Nominal

Diameter (DN = 50 mm in European system.

(1-2-2-2) Large valves:

They are valves whose diameters are equal or larger than 2 1/2

inch or 65 mm.

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(1-2-3) Classification By Pressure-Temperature Rating: Classification is designated by class numbers based on the


construction material, the pressure rating at temperature

ratings. The number denotes the maximum allowable working

gauge pressure of certain design at the selected rating

temperature of the mentioned code or standard, this

temperature is specified in accordance with the application.

For cold working applications (general service), this

temperature ranges from –20 to 100°F (-29 to 38°C) but for

fire application the rating temperature is higher than cold

working-rated value. So, at the same temperature a valve

specified for fire withstands higher pressure for example [A

valve of 175 psig (1210 KPa) rating pressure specified for fire

protection can be used for 400 psig (2760 Kpa) for cold

working or general service)]. By this way the valves are

classified according to the rating pressure for certain condition

as follows :-

(1-2-3-1) Cold Working (General Service) Pressure Rating :

Valves which are marked with CWP (Cold Working Pressure) or

WOG (Water–Oil–Gas) rating can be used for the marked

pressure rating (150, 300, 400, 600, 900, 1500, 2500, 4500 psig)

as the maximum allowable working pressure at ambient

temperature.

(1-2-3-2 )NFPA(National Fire Protection Association) Rating:

The valves which are used in fire protection system in (U.S.A)

are rated for fire service at a temperature higher than

ambient temperature and have different numbers than CWP

classification such as 175, 250 psig or 1210, 1725 kpa.

(1-2-3-3) Steam Working Pressure (SWP) Rating:

عل هذا العلم صدقة جاريه لروح من أعدهاللهم اج (12)

If the valve is marked with SWP, that means the valve is

specified based on steam service and the marked number

denotes the allowable pressure for the required steam.

(1-2-3-4) Dual or Multiple Rating :

The valve may be assigned one or more ratings by the valve manufacturer, these ratings must be marked on the valve as well as their applicable standard, for example a class 600,4 inch butt welding end, steel gate valve complying with ASME B16.34 may be marked as class 800 valve in accordance with API 603, this valve complies with the design and construction requirements of both ASME B16-34 and API 603. But in ASMI the factor of safety is greater than API.

* The Effect of Valve Material :

Valve material affects the class number, for the same design pattern of the ordinary material, this class shall increase for higher grade of materials at the same temperature rating. ASME 16.5 classifies the flanged fittings of piping system for each material group table B2.1 as shown in table B2.3 for matrial group1.1 in classes number.

ASME B16.5 provides seven pressure classes for flanges. They are Classes 150, 300, 400, 600, 900, 1500, and 2500. The pressure-temperature ratings for flanges representing all material groups are organized within 34 tables, one for each material group. Table B2.3 is adapted from ASME Standard B16.5 and is typical of the 34 flange rating tables. It provides the pressure-temperature ratings for flanges in material group 1.1. The table is organized with the pressure classes listed across the top and the maximum working temperatures along the left-hand border. The body of the table provides the pressure ratings for flanges from each pressure class, at the given temperature.

In practice, the use of ASME B16.5 to determine a flange rating is quite simple. The procedure is outlined below: 1. Determine the maximum operating pressure and temperature for the required flange. 2. Select a flange material and therefore a material group from one of the 34 listed material groups.

Be aware that some of the qualifying notes concerning maximum operating temperatures for various materials may influence the final material selection. 1. Determine the maximum operating pressure and temperature for the required flange. 2. Select a flange material and therefore a material group from one of the 34 listed material groups. Be aware that some of the qualifying notes concerning maximum operating temperatures for various materials may influence the final material selection. 3. Enter the appropriate material group table at the increment of temperature listed which is higher than the desired maximum operating temperature. Start with the Class 150 column and proceed to the right until a pressure rating for the desired temperature is found which equals or exceeds the required operating pressure. The column in which this condition is satisfied dictates the required pressure class and specifies the actual pressure-temperature rating of the flange.

Example B2.1. Assume that an ASTM A105 carbon-steel flange is required to satisfy a pressure rating of 1060 psig (7310 kPa gage) at 650F (343C). ASTM A105 is a material group 1.1 material. Entering Table B2.3 at a temperature of 650F (343C), a Class 600 flange is found to have a rating of 1075 psig (7420 kPa gage) at 650F (343C). Therefore, a Class 600 ASTM A105 flange is suitable for the stated conditions. When using the tables, linear interpolation between listed temperatures and pressures may be employed to determine intermediate pressure ratings.

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(1-2-4) Classification Based on the Main Function :

Each valve can be used for stop the liquid flow or a portion of it. There are some types more suitable for stopping the flow and others are more suitable for regulation, … etc. In this classification the valve is designated by its function as follows :

(1-2-4-1) Stop (Isolation) Valves:

This type is used to isolate a portion of piping system, the main feature of this type is to offer minimum resistance to flow in the fully open position and tight-off characteristics when fully closed, gate or ball valve is more suitable.


(1-2-4-2) Regulators: Regulators can be used in place of control valves when set point deviation is not critical. Regulators are a self-powered control valve but usually on a small scale. Regulators can be used where control valves would be used but external power is not available, such as in portable applications or in house gas bottle. Most control valves are pneumatic but increasing numbers of electric powered valves are being installed. A minority of control valves are hydraulically powered. All control valves require external power to be operated such as compressed air, electricity, hydraulic fluid. In some locations external power is not available and the cost of supply power is prohibitive. In some hazardous locations it may not be desirable to introduce electric supplies. A regulator can overcome all of these difficulties providing the process fluid is suitable at a pressure higher than set point. One of the most popular regulator applications is the reduction in pressure of bottled gas. Bottled gas is widely used for cooking, heating, industrial and medical purposes. These gases may include acetylene, butane, carbon dioxide, LNG, LPG, nitrogen, nitrous oxide, oxygen, and propane. Gas bottles usually contain pressurized liquid gas. The liquid pressure in the bottle is generally too high for the user and a regulator is fitted to allow a suitable pressure to be selected. Regulators are used extensively by the water and gas supply utilities. Fluid is transported over long distances in pipelines and the demand, ie. flow rate, can vary significantly. The variation in frictional losses would result in large pressure changes at the consumer outlets. Regulators are placed at strategic locations in local supply branches to minimize pressure excursions. Back pressure regulators, Vessels which store flammable liquids, and also compressor, engine and reciprocating pump crankcases, are often pressurized or purged with a safe gas

روح من أعدهاللهم اجعل هذا العلم صدقة جاريه ل (14)

such as nitrogen. The nitrogen, at a pressure slightly above atmospheric, displaces the air and forms a non-combustible safety blanket. The gas blanket also prevents the ingress of

dirt and moisture which could promote corrosion. (1-2-4-2-1) Regulator design: Regulators can be divided into two basic groups: * Diaphragm Operated Valves. * Piston Operated Valves. Both groups can be designed as a direct-acting and pilot-operated to cope with size, pressure and accuracy.

1- Diaphragm Operated Reducing Valve Design: This valve is used to reduce the available pressure to the required pressure for use, it is called direct-acting diaphragm regulator, see Figure 4(a) . The regulator is shown partially open and fluid enters from the left. The downstream port of the regulator communicates with the underside of the diaphragm via a small port. The spring case above the diaphragm is vented to atmosphere. The regulator set point is adjusted by modifying the adjusting screw. Increasing the spring force increases the set point and vice-versa. If the downstream pressure is low the spring force overcomes the diaphragm force and opens the regulator.

Figure 4(a): Direct-acting diaphragm pressure reducing regulator

The lower the pressure the wider the regulator opens. As the


downstream pressure approaches the set point the diaphragm force increases and gradually compresses the spring. If the set point is reached the regulator closes and prevents further flow.Diaphragm regulator is a very simple device. The diaphragm is clamped between the "valve" body and the spring case. Diaphragms can be metal as well as elastomer. Friction of the guidance and stiffness of the diaphragm tend to reduce accuracy but impart damping to reduce "hunting". The diaphragm area can be increased to compensate for friction and stiffness; but this introduces increased inertia which creates opening "over-shoot" and valve closing impacts, unless porting and spring modifications are incorporated Double-beat globe valve designs Fig 37 can be used to reduce the spring and diaphragm forces required to operate the regulator. The regulator characteristic can be modified in various ways. The valve plug can be profiled as in a control valve. Standard helical coil springs have a constant spring rate. An increasing spring rate can be produced by winding the end coils at reduced pitch. This would reduce regulator opening with pressure variation. The communication port can be adapted to suit varying operating conditions. Throttling, fixed or adjustable, can be added. Multiple ports can be used, some with non return valves; this allows faster opening or closing. The diaphragm can be replaced by a metal bellows. Both elastomer/metal diaphragms and metal bellows can suffer from fatigue problems. The fluid and operating conditions must be fully evaluated when selecting materials and the type of construction. These styles of regulators can be used for inlet pressures up to 415barg in the smaller sizes that extend to DN50. For clean fluids, a piston or spool pressure reducing regulator may be used. Depending upon the nature of the fluid, it may be possible to eliminate all non-metallic materials


to allow high temperature operation. Figure4(b) shows a one.

2- Piston-Operated Reducing Valve Design: The piston regulator Fig 4(b) is very similar to the diaphragm version.

Figure 4(b): Direct-acting piston pressure reducing regulator When piston seals are used, they increase the friction forces tending to impair movement and also increase damping. Metal pistons have more inertia than diaphragms and this effect can increase any "over-shoot" or hard closing problems. Generally, when direct-acting regulators become larger the problems of inertia and diaphragm stiffness increase and accuracy is sacrificed. The problems can be overcome by using a pilot-operated regulator.

a- (just when theoutlet pressure decreases) (17) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

b- ( the disk fluctuates between closing and opening )

Figure 5: A pilot-operated diaphragm pressure reducing regulator The pilot is a small diaphragm regulator, of the type shown in Figure 4(a), is used to sense the control signal. The flow from the pilot is directed to the underside of the much larger diaphragm in the main valve. If the downstream pressure falls the pilot valve opens Fig 5(a) allowing upstream process fluid to flow under the main diaphragm, this unbalances the main diaphragm and increases the main valve open, then more process fluid flows downstream to increase the outlet pressure up to the set point at which the pilot valve closes Fig 5 (b) and the two diaphragm are affected only by downstream pressure and remain at this position until the downstream flow rate increases and in turn the downstream pressure decreases permitting the pilot valve opens to readjust downstream pressure and so on. Pilot-operated regulators should be used when an accuracy of better than + 5% of set point is required or the valve size is over DN50. DN 150 is the largest popular pilot-operated regulator size for general process applications. Cast iron regulators, specifically for water applications, are readily


available up to DN300. The manufacturer's specification should be checked before finalizing the pipework design because the regulator will generally be smaller than the nominal pipe size used, so allow space for reducers. Pressure regulators are designed in different sizes, materials, and components to be suitable for specified fluid and pressures, table 2 lists typical pressure reduction regulators.

Table 2 :Typical pressure reduction regulators

(1) A = air, G = gas, L = liquids, O = oil, S = steam, W = water (2) A = aluminum, B = brass, BRZ = bronze, CI = cast iron, CS = carbon steel, DI = ductile iron, SS = stainless steel (3) Hygienic applications with CIP or SIP. (4) Altitude valve.

لم صدقة جاريه لروح من أعدهاللهم اجعل هذا الع (19)

(1-2-4-2-2) Back Pressure Regulator: Back pressure regulators maintain the upstream pressure at a constant value. The regulator acts as a dump valve when the pressure is too high, and fluid is allowed to flow to a lower pressure system. If the pressure is low the regulator closes to try to maintain the pressure. Some types of this regulator are designed to be used as relief valves.

(1-2-4-2-3) Differential pressure regulator: The differential pressure regulator tries to maintain a constant differential pressure between the regulator inlet and outlet pressures. This type of regulator is used extensively in the water distribution industry. Cast iron globe valve bodies are extended to include the lower diaphragm casing. The valve disc is also extended to provide support and a connection to the diaphragm.

Figure 6: Typical differential pressure regulator for water


An external differential pilot controls the water flow above the diaphragm. Water industry regulators use copper pipework for the pilot and bronze or brass fittings. These regulators are available in sizes up to DN300 for pressure ratings up to PN25. The differential pressure can be adjusted between 0.14 barg and 17.24 barg. Figure 6 shows a schematic arrangement of a typical valve. As the regulator outlet pressure decreases, the outlet pressure and spring force move the pilot diaphragm downward to enlarge its open and decrease its inlet pressure which is acting above the regulator diaphragm to move it upward and also enlarges the regulator open then decreases the inlet pressure by the same value of the outlet, and vice versa. Table 3 shows some of the more popular pressure reducing regulators available.

Table 3 :Typical differential pressure reducing regulators

(1) A = air, G = gas, L = liquids, O = oil, S = steam, W = water (2) A = aluminum, B = brass, BRZ = bronze, CI = cast iron, CS = carbon steel, DI = ductile iron, SS = stainless steel

(1-2-4-2-4) Constant flow regulator: constant flow regulator is a differential pressure regulator. Flow sensing is added as the controlling differential pressure. Usually an orifice plate is fitted to the valve inlet. Pilot constant flow regulators are very similar to that shown in Figure 6. The differential pressure signal from the orifice plate is applied directly across the pilot diaphragm..


For water applications the regulator body will be cast iron for pressure ratings up to PN (pressure nominal) 25 = 25 barg. Fabric reinforced nitrile rubber is standard for diaphragms. The valve plug generally has a rubber insert to improve sealing qualities. Sizes range from DN15 to DN300. Pilot operated regulators can cope with maximum flow rates between 19.5 to 1180m3/h. Small direct-acting constant flow regulators are produced specifically for high pressure water applications. Sizes are usually up to DN50 for maximum pressures of 345 barg. The differential pressure across the regulator is limited to between 1.7 and 3.4 bar. The standard body material is carbon steel.

(1-2-4-2-5) Excess flow shut-off valve: Excess flow shut - off valve is an isolating valve which is flow sensitive. Under normal operating conditions the valve is open and fluid flows with a slight pressure drop. In the event of process control failure or pipe/vessel fracture the normal fluid flow rate can increase dramatically and very serious consequential damage can ensue. Incorrect proportions of chemicals being mixed can lead to devastating results. Fluids flowing from open pipes and vessels can create dire personnel hazards or permanent environmental damage, costly products can be lost forever. The excess flow shut-off valve senses fluid velocity higher than required and isolates the system. The higher fluid velocities create increased fluid drag within the valve and produce sufficient force to close the valve. Figure 7 shows a typical liquid excess flow design. Valves up to DN600 have been produced. Pressure ratings are not a problem as the valve body has no openings around the periphery. Valves can be manufactured in most materials to suit the process. Once closed, the excess flow shut-off valve must be reset before it will open. To reset the valve, the pressure on both sides must be equalized; this can easily be achieved by a small by-pass.


Figure 7: A typical liquid excess flow shut-off valve

============================================= (1-2-4-3) Check Valves {Non-Return Valves(nrvs)}: Non-return valves, or nrvs as they are known, prevent fluid from travelling the wrong way in systems. A popular application is to prevent circulation in rotodynamic compressors and pumps, because most pipe systems include changes in pipe elevation, which require the rotodynamic machine to impart some static head to the fluid which pressurizes the system. When the machine stops the static head decays as a result of the fluid returning to the lowest points in the system. A non-return valve can prevent the fluid from returning to the suction source. However the reverse flow can cause serious machine problems. Lube oil pumps driven from the machine spindle may not supply any lube oil when running backwards. Running at any speed in reverse can cause costly damage to bearings and gearing. In complex systems, where good reliability and continuity of production must be assured, multiple rotodynamic machines are installed. Some machines will run continuously while


others will be on stand-by in case a fault develops. In some processes the stand-by machines must take over almost instantaneously. There is no time for an operator to manually open isolating valves or even wait for power-actuated valves to open. The stand-by machine must be ready to run as soon as an operator presses the start button or the process control system initiates the start sequence. A non-return valve provides a good solution. The running machines discharge into the system. The higher pressure fluid is prevented from returning to the suction source through stationary machines by nrvs. The failed running machine can then be isolated and inspected or repaired while production continues. Some positive displacement machines need to be fitted with nrvs in a similar way to rotodynamic machines. The following machine types should be fitted with non-return valves when used in a stand-by situation: Gear, Lobe, Screw, Rotary piston, and Vane Machines. The type and size of the non-return valve which must be fitted in a system can be greatly influenced by the necessity of cleaning or inspecting the pipework with a "pig". If"pigging" is a prerequisite then the non-return valve must be able to present a completely clear bore of approximately the same diameter as the pipe. A slightly larger bore would be acceptable, but not a smaller one. Finally, it may be necessary to fit protection for the non-return valve or instrumentation to indicate correct function or valve status. Clean fluid systems are only clean after flushing and some time of normal operation. Systems which operate with a degree of solids content frequently have unexpected solids in the worst possible locations. Crude oil , specified to contain sand, sometimes contains pebbles. Equipment selected to pass sand up to 2mm may be damaged or disabled by 10mm pebbles.


Nrvs fitted to stand-by machines can be a considerably drain on energy if the valve is permanently "cracked-open" by sand on the seat. Permanent instrumentation may not be necessary if maintenance staff perform routine inspections with modern equipment. The high frequency acoustic signal created by a high velocity fluid passing through a small aperture should be easily detected.

(1-2-4-3-1) Non-Return Valve Design: The non-return valve is an automatic, self-powered valve which tries to ensure fluid only moves in one direction. The moving element normally rests on the seat to form a seal. A small pressure must be applied to the moving element to open the valve initially. Once open, fluid-dynamic forces are generated which hold the valve open or increase the opening. Fluid flow must usually stop before the valve will close. The fluid-dynamic forces created by any fluid flowing across the seat will generally prevent all valves closing. Springs may, or may not, be used to control opening and assist closing. Some valves rely solely on gravity to provide the closing forces. Valves which rely on gravity must be installed according to the manufacturers' instructions. Swing disc valves are gravity-powered. As the valve opens, the force required to hold the valve open increases. If the balance between disc mass and fluid-dynamic forces is incorrect the valve will not open completely. Increased fluid velocities may result in unexpected corrosion or erosion damage. Gravity- powered valves must be matched to the fluid and operating conditions. When valves open fully, the disc or piston travel must be limited by a stop. Valves which open fully, but are not stop limited, are liable to "flutter". Flutter can cause rapid wear of hinge pins or piston guides. Valves which use springs can suffer from early spring failure due to fatigue. Flutter can be

اجعل هذا العلم صدقة جاريه لروح من أعده اللهم (25)

caused by the shedding of eddies, or turbulence. Damping can be used to restrict the flutter movement. Fluid damping, using squish, can be effective when the fluid has some viscosity. Valves using springs can have variable rate springs fitted. If the full travel stop incorporates squish, to prevent rebound after rapid opening, this can be an effective flutter damper. Squish can be incorporated into the seat and disc/piston design to prevent the valve slamming shut. Extra material is added around the seat contact area to create two squish zones. Trying to squeeze the fluid out of these zones during rapid closure slows the valve down. But there is a penalty to be paid. The increased area of limited clearance is an ideal site for trapping small solids. Squish protection for damped closure can lead to more problems caused by trapped solids, unless there is adequate clearance for the squish action to eject the solids. Valves with narrow seats can crush friable solids, such as coal. The squish zones tend to broaden the effective seat width and reduce the valve's capability to crush solids. This effect must be considered, taking into account the nature of any pertinent solids. The problem of flutter may be restricted to small valves. As valves become larger the inertia of the moving parts becomes much greater. The increased inertia can effectively dampen flutter and lead to delayed closure, after reverse flow has commenced. Damping at the seat therefore becomes very important. As with all valves, the flow areas must be checked and velocities calculated for design operating conditions. Areas around discs and pistons are as important as the main port areas. Flow areas which are smaller than others will be the zones where erosive, and possibly cavitation wear, will occur. Non-return valve bodies can incorporate extra connections for special functions such as venting and draining. Valves for hot


applications can sometimes be fitted with an external by-pass to allow system preheating at low flows. The pressure of the fluid passing through the system opens the valve, while any reversal of flow will close the valve. Closure is accomplished by the weight of the check mechanism, by back pressure, by a spring, or by a combination of these means. Most of check bodies are made of one-piece and may be mass produced in the specifications shown in table 4

Table 4 : One-piece body, swing disc non-return valve materials and ratings

(1-2-4-3-2) Check Valve Types: The general types of check valves are swing, tilting-disk, piston, butterfly, and stop.


1- Swing Check Valves: A swing check valve is illustrated in Figure 8. The valve allows full, unobstructed flow and automatically closes as pressure decreases. These valves are fully closed when the flow reaches zero and prevent back flow. Turbulence and pressure drop within the valve are very low. A swing check valve is normally recommended for use in systems employing gate valves because of the low pressure drop across the valve.

Figure 8: Swing Check Valve

Swing check valves are available in either Y-pattern or straight body design. A straight check valve is illustrated in Figure 9. In either style, the disk and hinge are suspended from the body by means of a hinge pin. Seating is either metal-to-metal or metal seat to composition disk. Composition disks are usually recommended for services where dirt or other particles may be present in the fluid, where noise is objectionable, or where positive shutoff is required. Straight body swing check valves contain a disk that is hinged at the top. The disk seals against the seat, which is integral


with the body. This type of check valve usually has replaceable seat rings. The seating surface is placed at a slight angle to permit easier opening at lower pressures, more positive sealing, and less shock when closing under higher pressures. Swing check valves are usually installed in conjunction with gate valves because they provide relatively free flow. They are recommended for lines having low velocity flow and should not be used on lines with pulsating flow when the continual flapping or pounding would be destructive to the seating elements. This condition can be partially corrected by using an external lever and weight.

2- Tilting Disk Check Valves: The tilting disk check valve, illustrated in Figure 9, is similar to the swing check valve. Like the swing check, the tilting disk type keeps fluid resistance and turbulence low because of its straight- through design. Tilting disk check valves can be installed in horizontal lines and vertical lines having upward flow. Some designs simply fit between two flange faces and provide a compact, lightweight installation, particularly in larger diameter valves. The disk lifts off of the seat to open the valve. The airfoil design of the disk allows it to "float" on the flow. Disk stops built into the body position the disk for optimum flow characteristics. A large body cavity helps minimize flow restriction. As flow decreases, the disk starts closing and seals before reverse flow occurs. Backpressure against the disk moves it across the soft seal into the metal seat for tight shutoff without slamming. If the reverse flow pressure is insufficient to cause a tight seal, the valve may be fitted with an external lever and weight.


Open Closed

Figure 9: Operation of Tilting Disk Check Valve(3-Piece Body)

These valves are available with a soft seal ring, metal seat seal, or a metal-to-metal seal. The latter is recommended for high temperature operation. The soft seal rings are replaceable, but the valve must be removed from the line to make the replacement.

3-Lift Check Valves: A lift check valve, illustrated in Figure 10, is commonly used in piping systems in which globe valves are being used as a flow control valve. They have similar seating arrangements as globe valves. Lift check valves are suitable for installation in horizontal or vertical lines with upward flow. They are recommended for use with steam, air, gas, water, and on vapor lines with high flow velocities. These valves are available in three body patterns: horizontal, angle, and vertical. Flow to lift check valves must always enter below the seat. As the flow enters, the disk or ball is raised within guides from the seat by the pressure of the upward flow. When the flow stops or reverses, the disk or ball is forced onto the seat of the valve by both the backflow and gravity.


Some types of lift check valves may be installed horizontally. In this design, the ball is suspended by a system of guide ribs. This type of check valve design is generally employed in plastic check valves. The seats of metallic body lift check valves are either integral with the body or contain renewable seat rings. Disk construction is similar to the disk construction of globe valves with either metal or composition disks. Metal disk and seat valves can be reground using the same techniques as is used for globe valves.

Figure10: Lift Check Valve

4- Piston Check Valves: A piston check valve, illustrated in Figure 11, is essentially a lift check valve. It has a dashpot consisting of a piston and cylinder that provides a cushioning effect during operation. Because of the similarity in design to lift check valves, the flow


characteristics through a piston check valve are essentially the same as through a lift check valve. Installation is the same as for a lift check in that the flow must enter from under the seat. Construction of the seat and disk of a piston check valve is the same as for lift heck valves. Piston check valves are used primarily in conjunction with globe and angle valves in piping systems experiencing very frequent changes in flow direction. Valves of this type are used on water, steam, and air systems.

Figure 11: Piston Check Valve

5- Butterfly Check Valves: Butterfly check valves have a seating arrangement similar to the seating arrangement of butterfly valves. Flow characteristics through these check valves are similar to the flow characteristics through butterfly valves Consequently, butterfly check valves are quite frequently used in systems using butterfly valves. In addition, the construction of the


butterfly check valve body is such that ample space is provided for unobstructed movement of the butterfly valve disk within the check valve body without the necessity of installing spacers .The butterfly check valve design is based on a flexible sealing member against the bore of the valve body at an angle of 450. The short distance the disk must move from full open to full closed inhibits the "slamming" action found in some other types of check valves. Figure 12 illustrates the internal assembly of the butterfly check valve. Because the flow characteristics are similar to the flow characteristics of butterfly valves, applications of these valves are much the same. Also, because of their relatively quiet operation they find application in heating, ventilation, and air conditioning systems. Simplicity of design also permits their construction in large diameters - up to 72 inches. As with butterfly valves, the basic body design lends itself to the installation of seat liners constructed of many materials. This permits the construction of a corrosion-resistant valve at less expense than would be encountered if it were necessary to construct the entire body of the higher alloy or more expensive metal. This is particularly true in constructions such as those of titanium.

Fig12 : Butterfly Check Valve


Flexible sealing members are available in Buna-N, Neoprene, Nordel, Hypalon, Viton, Tyon, Urethane, Butyl, Silicone, and TFE as standard, with other materials available on special order. The valve body essentially is a length of pipe that is fitted with flanges or has threaded, grooved, or plain ends. The interior is bored to a fine finish. The flanged end units can have liners of various metals or plastics installed depending upon the service requirements. Internals and fasteners are always of the same material as the liner.Butterfly check valves may be installed horizontally or vertically with the vertical flow either upward or downward. Care should be taken to ensure that the valve is installed so that the entering flow comes from the hinge post end of the valve; otherwise, all flow will be stopped.

6- Stop Check Valves: A stop check valve, illustrated in Figure 13, is a combination of a lift check valve and a globe valve. It has a stem which, when closed, prevents the disk from coming off the seat and provides a tight seal (similar to a globe valve). When the stem is operated to the open position, the valve operates as a lift check. The stem is not connected to the disk and functions to close the valve tightly or to limit the travel of the valve disk in the open direction.

7- Non-return foot valve: Foot valves are a special type of non-return valve, intended for the suction pipes of pumps. Most pumps require priming before starting. Priming involves filling the pump casing with liquid and expelling any trapped air. Some pumps are self - priming and these pumps will be specifically described as such. Even these pumps need some liquid in the pump casing to be able to work properly.


Fig 13: Stop Check Valve

The footvalve is designed to maintain the suction pipework and the pump casing full of liquid. Foot valves are used on pump installations where the pump lifts liquid from a source below the pump. The pump casing and the suction pipe can be filled manually by pouring liquid into the pump. Alternatively the liquid can be induced into the pipework and casing by applying a vacuum to the casing. In both cases the foot valve prevents the liquid running straight out and emptying the casing. It must be remembered that a foot valve is a resistance in the suction system and results in a loss of suction pressure and


NPSHa/NPIPa for the pump. The resistance must be considered when designing the pipework and selecting a valve. There are many types of non-return foot valve to suit many applications: plate, poppet Fig 14 , bali, flat diaphragm, and tube diaphragm.

Fig 14 : Poppet foot non-return foot valve

All valve types may be fitted with a suction strainer; the design of the strainer being dependent upon the pump application. Contractors' pumps, i.e. those pumps used on building sites to drain ditches and pits, may be suitable for handling solids up to 100mm. The strainer must limit the solid intake to the pump's capacity. A heavy duty wire cage is necessary. Process pumps generally operate with clean liquids. A perforated metal tube or woven wire mesh, of adequate flow area, is adequate.

============================================ (1-2-4-4) Relief and Safety Relief Valves: High pressure systems and pressure vessels may be subjected to excess pressures , if this pressure exceeds the design


pressure , it will cause material over-stressing. The nature of the system and its environment must be analyzed to evaluate the size of the pressure problem. Problems due to temperature rise due to fire or hot sun rays or chemical reactions errors can result in excess pressure. Positive displacement pumps and compressors are capable of generating very high pressures which must be avoided if the piping system resistance increases. Systems are usually protected against excess pressure. Safety valves can be fitted to prevent pressures above a predetermined value being applied. Operation above the set pressure is considered as emergency condition which should be rectified very quickly. If process operation or control dictates extended running over the set pressure, the time period must be evaluated to compressor or pump manufacturer and the valve manufacturer. Excess pressure protection can sometimes be unnecessary if the source of pressure (pump, compressor) can be controlled directly. Any pressure relief device which is fitted must be reliable. Reliability can be increased by the use of simple equipment, spring-loaded and dead-weight safety valves are among the simplest machine elements in current use. Standard spring-loaded relief and safety relief valves are not suitable for shock wave protection. Explosion relief valves are specifically designed for protection against shock waves but are usually only suitable for pressures close to atmospheric. Shock waves travel through the fluid at acoustic velocity, when passing the valve, the local pressure causes the valve to open. If the shock wave is severe the valve may slam wide open. The pressure is only applied momentarily as the wave passes. There is no fluid flow associated with the shock wave, so there are no hydrodynamic forces developed to keep the valve open, but the valve closes as violently as it opened.


Violent closing can damage the disc and the nozzle leading to leakage of product. Pilot-assisted valves, or pilot-operated valves, may be able to withstand the worst effects of violent closure by holding the valve open for a fixed period followed by controlled closure. Shear pin, buckling pin safety valves, and bursting discs may open allowing product to escape. All operating conditions, including process upsets and possible shock wave generators, must be properly evaluated when selecting valves. The use of variable speed drivers for compressors and pumps has resulted in increased demands for the more complex relief valves. (1-2-4-4-2) Difference between a Relief and Safety relief valve: The main difference between a relief valve and safety relief valve is the extent of opening at the setpoint pressure. A safety relief valve will stay fully open until the pressure drops below a reset pressure. The reset pressure is lower than the actuating pressure setpoint. The difference between the actuating pressure setpoint and the pressure at which the

safety valve reseats is called blowdown. Blowdown is

expressed as a percentage of the actuating pressure setpoint. Relief valves are typically used for incompressible fluids such as water or oil. Safety relief valves are typically used for compressible fluids such as steam or other gases. Safety relief valves can often be distinguished by the presence of an external lever at the top of the valve body, which is used as an operational check. Most relief and safety relief valves open against the force of a compression spring. The pressure setpoint is adjusted by turning the adjusting nuts on top of the yoke to increase or decrease the spring compression.

A relief valve, illustrated in Figure 15, gradually opens as the inlet pressure increases above the setpoint then the system pressure overcomes spring pressure and the relief valve opens to relieve the over-pressure condition. As the


system pressure is relieved, the valve closes when spring pressure again overcomes system pressure.

A safety relief valve, illustrated in Figure 37, rapidly pops fully open as soon as the pressure setting is reached. As indicated in Figure 16, system pressure provides a force that is attempting to push the disk of the safety valve off its seat. Spring pressure on the stem is forcing the disk onto the seat.

INLET

Fig 15: Relief Valve (39) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

Fig 16: Safety Valve

(1-2-4-4-3) Safety relief and relief valve design: Safety relief and relief valves are similar in design and became essential to protect equipment and personnel from higher operating pressures.


(a): Simple dead-weight relief valve

(b) Dead-weight lever relief valve (c) Open spring-relief valve

Figure (17)

The first relief valves were dead-weight, it is a mass resting on the valve disc held the valve closed, see Figure 17(a). The valve could only be mounted vertically. Fluid pressure acting over the nozzle area created a force trying to lift the disc. The weight of the disc, plus additional weights, resisted the steam force. The valve could be easily adjusted to very accurate set points while operating. This type of valve was very reliable and effective. Because the valve only had three components, so the number of failure modes were very limited. The earliest safety relief valves were designed for low pressure steam. As steam pressures

ح من أعدهاللهم اجعل هذا العلم صدقة جاريه لرو (41)

increased, improvements were necessary and the dead-weight lever valve was developed, see Figure 17 (b) the addition of leverage to the relief valve design allowed higher pressures to be contained while maintaining the nozzle area constant , the valve set pressure could be adjusted by the addition of small weights or by moving the large weight on the lever, so that one size of valve could be made suitable for many operating conditions, but the space required for the relief valve also increased. A new style of valve was therefore needed. Advances in material manufacture allowed springs to be produced. The dead-weight lever relief valve was replaced by an open spring relief valve, Figure 17(c) . The valve disc became an extended poppet which was top and bottom guided. The seating could be angled, as shown, to aid centralisation, or flat. The spring load was adjusted by varying the pre-compression. Shims could be added under the yoke to increase the set pressure. Small increases in set pressure could be accomplished by adding weight on top of the spindle. The spring-loaded relief valve was very compact and a fixed nozzle area could be used for a wide range of pressures by varying the spring design.

(1-2-4-4-4) Safety relief valve Design: Safety valves, or bursting discs, can be fitted to prevent pressures above a predetermined value being applied. Figure 18 indicates the relationship between the various pressures for a group of safety valves: *Conventional group (1) * Pilot-assisted group (2) *Supplementary loaded group(3) * Pilot-operated group (4)


Normal operating pressure is indicated as 100%. The typical ranges of set pressure (S), overpressure (O) the pressure at which the valve Passes 100% of its flowrate, and blowdown (B) the pressure at which the valve starts closing. Conventional spring-loaded valves are greatly influenced by the fluid properties, and to some extent by the inlet and outlet pipework.

Figure 18: Operating pressures for safety relief valves

More complex, and costly, valve designs allow the minimum set pressure to be moved closer to the normal operating pressure, although a special conventional valve, with a resilient seat, does allow low set and overpressure operation. Some designs allow the overpressure to be drastically reduced. The figure also shows that the blowdown can be adjusted over a very wide range and this point must be carefully considered. Two aspects of valve operation must be considered in the context of valve cycling (cycle= open then close): *Does the valve close at a pressure between the normal and set?


*Does the system pressure have to reduce below the normal pressure for the valve to close? If the valve closes too soon the fault condition may not havebeen rectified and the valve will re-open immediately. Valve cycling causes wear and if very rapid pressure changes are involved can damage the nozzle and disc. Valve cycling is dependent upon the process system characteristics and must be evaluated on a case-by-case basis. Pilot-assisted and pilot- operated valves can help to alleviate this problem by holding the valve open for a specific time every time the valve opens. As with controlled closure, the wear and damage problems can be greatly reduced. However, the valve life is extended at the cost of wasted product. Positive displacement compressors and pumps, without instructions to the contrary, operate intermittently at any pressure above the set pressure. This time period cannot be quantified as it is dependent upon: *The running conditions immediately prior to fault. * The running time prior to the fault. * The size and type of the driver. Operation above the set pressure is considered as an emergency condition which should be rectified very quickly. If process operation or control dictates extended running over the set pressure, the time period must be evaluated and communicated to the compressor/pump manufacturer and the valve manufacturer. Positive displacement machines can create pressure pulsations in the process system. The peak-to-peak value of the pulsations is dependent upon the system design and the fluid as well as the machine design and speed. When selecting the relief valve set pressure, the magnitude of the positive peak must be considered and an allowance made to avoid spurious valve operation. Pulsation dampers may be fitted to the machine to reduce peak-to-peak values.


Some rotodynamic machines produce undesirable pressure pulsations at certain operating conditions. This factor must be considered if relief valves are fitted for system protection. When considering the use of a safety valve, the energy of the system and the rate at which energy is added to the system plays an important part. Some systems can produce very high pressures at low energy levels. The pressures are high enough to fracture pipework and fittings but the energy levels are so low that personnel are not put at risk. Such systems include single-shot lubrication systems and diesel injection systems on small engines.When two processes react physically but are not normally incontact, for example two fluids in a heat exchanger, the otherfluid may influence safety requirements. Some chemical processes place special demands on safety valve sizing. Vessels in which reactions, separation or evaporation take place require detailed study. Precautions must be taken if the fluid may change phase while passing through the valve or if the fluid could be multi-phase when entering.

(1-2-4-4-5) Safety relief valve types: (1-2-4-4-5-1) Spring-Loaded Valves for Gas, Vapor and Steam: The modern spring-loaded valve is similar to that shown in Figure 37. The valve could suffer from drainage problems. The large valve is not self-draining and a drain plug is provided, then a piped drain may be appropriate at site. The small valve may be self draining depending upon the exact details of the body. Metallic materials in contact with hydrogen sulphide, H2 S, are liable to corrode and suffer sulphide stress cracking. Hardened materials, like the nozzle and disc, are more prone than soft materials. The spirit of NACE is to avoid hardened materials and crevices where sediment can accumulate. A screwed thread is effectively a long crevice. The problem of


the crevice can be solved by fitting a seal to protect the thread. Socket weld construction would not be suitable for NACE applications. NACE gives guidance on suitable hardened materials and heat treatments. On flanged valves fig 19 the nozzle may be a clearance fit in the body rather than screwed. This is particularly convenient in situations when the nozzle may have to be replaced regularly due to corrosion or erosion damage.

دقة جاريه لروح من أعدهاللهم اجعل هذا العلم ص (46)

Figure 19 : Typical flanged safety relief valve

Most safety relief valves have one outlet slightly larger than the inlet. Bodies with two outlets may be necessary to cope with some very compressible fluids or large differential pressures. The larger flanged valve has a screwed blowdown ring on the outside of the nozzle. This ring is used to adjust the overpressure and the blowdown pressure. At the highest pressure the spring is compressed the most and is subjected to the highest stresses in closing positions. The spring must have sufficient clearance to allow the valve to open fully without becoming coil bound. Spring-loaded valves can suffer instability at low flows. Instability, caused by uneven or erratic flow patterns around the disc, can cause chatter or flutter resulting in, a rapid wear or worse damage to the disc and nozzle. If the inlet pipe pressure drop too high or the flow is restricted the valve will cycle causing either flutter or chatter, short pipework on both inlet and outlet is preferred. Normal metal-to-metal seats will leak, API 527 has specified maximum leakage rates depending upon the nozzle size and the set pressure for commercial quality valves. Figure 20 shows the allowable leakage when tested with air at 90% of the set pressure. This test is conducted after the valve has been "popped" and the leakage is to atmospheric pressure. A bubble is defined as 0.018 in3 or 0.295ml.


Figure 20: Safety relief valve leakage rates

Safety relief valves are generally constructed with cast bodies and may be from solid bar depending upon the size and the pressure ratings. Most standard designs anticipate the outlet pressure to be low, below 20 barg , regardless of the inlet pressure. Flanged valves for high back pressures tend to be special. Some manufacturers use castings which produce flanges which are thicker than the specification requirements. This is good from the point of view of valve body strength and rigidity and being able to withstand angular piping flange misalignment. However it does mean that special, extra long bolts or studbolts are essential. Most valve styles are manufactured in standard material combinations approximating to: cast iron with steel/bronze trim, bronze with bronze/stainless steel trim, steel with stainless steel trim, stainless steel with stainless steel trim. Ductile cast iron and steel bodied valves can be lined with corrosion resistant thermoplastic, PFA or PVDF, to broaden the range of applications. The nozzle and disc can be carbon-


fibre reinforced PTFE, virgin PTFE or exotic metal alloys. To prevent corrosive fluid entering the spring case, a PTFE bellows is fitted. The bonnet and cap will generally be cast iron, bronze or steel unless operating conditions, corrosion or temperature, make them unsuitable.

=========================================== (1-2-4-5) Pilot-Operated and Solenoid Valves: Pilot-operated valves Fig 21 are designed to open and close by a fluid pressure acting on a surface of two opposed pistons which are being connected to the valve stem and are operated by fluid coming from a pilot called solenoid valve according to electrical control signal.

Fig 21: Pilot-Operated Valve

======================================== (1-2-4-6) Solenoid Valve: Solenoid valves are usually small magnetically operated isolating valves. Figure 22 shows a typical direct-acting valve. The metal body,


is cast in one piece. The body has an upper bonnet inside which, the solenoid armature slides to open and close the valve by a bottom face sealing on the body seat.

Fig 22: Three- Port Solenoid Valve

Valves which are normally-open {NO} ( open when its coil is de-energized) , have a spring under the armature to hold the valve open. In normally-closed, (NC) valves ( closed when its coil is de-energized) the spring is on top. The electric coil, which creates the operating magnetic field, is located around the stainless steel enclosure. Coils are normally energized for the whole period of operation against the spring. Small valves may be bidirectional or unidirectional, so the manufacturers' instructions should be consulted. Some valves require a minimum inlet pressure to work; so specifications should be checked carefully. Solenoid valves are normally isolating valves with two ports, an inlet port and an outlet port. These valves may be called a


"two-way" solenoid valve and designated "2/2" followed by NC(Normal Closed) or NO (Normal Open). Solenoid valves can be designed with three ports Fig 22 for diverting applications, and is called "three-way" valves, designated "3/2" followed by NC. or NO., energizing the coil exchanges outlet ports. (if the third port is blocked the valve will be two port valve). The coils for solenoid valves are very important. Because coils

are electrical, they require, physical protection, insulation, duty rating, and power supply. Physical protection means fully protected against dust and intermittent immersion in water. The quality of the coil insulation determines how hot the coil can operate without damage. Class "F" insulation: 40o C ambient air, 100o C temperature rise, is fairly standard. Class "H" insulation: 40o C ambient air, 125o C temperature rise, is available on some heavy duty industrial valves. The duty rating is a factor for successful long term operation. If the coil is to be energized for long periods then a continuous or 100% rating is essential, some coils are only rated for 30%, 18 minutes per hour. The power supply for the coil can vary greatly. The following are very common; 12 Vdc, 24 Vdc, 110 Vdc, 220 Vdc, 24 Vac, 36 Vac, 48 Vac, 110 Vac, 220 Vac, 240 Vac, 380 Vac. Frequency of alternating current supplies is important. Coils for dc canhave a rectifier built-in to use on an ac supply. Coils do not consume much power, typically between 10 and 20 W. Solenoid valves are available in many body materials and sizes. Table 5 lists typical sizes and rating pressure.


Table 5 : Typical solenoid valve sizes and pressure ratings

Fig 23(a) , (b) shows application of pilot-operated valve and solenoid valves together in a pneumatic start system of gas turbine.

Fig 23 (a): Pilot- Operated Valve Is Closed


Fig23 (b):Pilot-Operated Valve Is Open

**********************************************

(1-2-5) Classification By the Closure Element Shape :

This is the most popular classification, so we are nominating

some valves by the shape of their closure element.

The most important parts in the valve are, the closure element

and its seat. The closure elements may have different shape as

follows :-


(1-2-5-1) Gate Valve :

This valve is illustrated in fig (24) in this valve, to stop fluid flow, a disc looks like a gate is moved crossing the stream lines of the flow through the valve, the gate is guided by two side seats tightened around the gate, the movement should be continued until the gate close the flow passage through the valve completely.

(1-2-5-1-1) Gate Valve Design: Valves are designed to prevent the contents leaking out. Some are designed specifically for vacuum applications when precautions must be taken against the atmosphere leaking in. Not all packing arrangements are suitable for both conditions, so specifications must be checked by designers. Valves are designed in a similar way to pressure vessels. The internal or external pressure produces a stress in the body wall material. The designer decides on a suitable safe stress and adjusts the wall thickness to suit. Manufacturing techniques, such as casting, may mean the wall thickness must be thicker than necessary, the spare material can be used as a corrosion allowance. When a pressure vessel code is applied to the design the allowable working pressure may increase or decrease to accommodate the code allowable stress. When a valve is fitted with flanges the body should be designed to match the flange ratings. Pressure vessel codes and flange specifications are very useful because the pressure-temperature relationships are tabulated for many materials. Non-metallic components, such as seats and seals must also be considered, when deciding extreme operating conditions.


Valves are designed for steady-state conditions in which temperature and pressure change slowly and without cyclic pulsation. If a valve is to be subject to rapid temperature changes , thermal shock may occur causing cracking. If pressure is going to change rapidly the shock load may break components or spring joints. If the pressure is going to pulsate cyclically then fatigue may result. Operation under non steady-state conditions must be taken in design consideration and should be discussed with the user. Valves can be designed to seal in both flow directions or only in one direction if they are used for one direction and they will normally have an arrow on the body indicating the direction of flow. Some valves achieve sealing by some form of wedging action. When open, one or more components may be "loose" and easily rattled by vibration. This can be a serious problem with pulsating fluid flow from all types of compressors and pumps, obviously this aspect of operating conditions must be considered when the designer selects a valve type. Non-metallic materials are very useful for low pressure corrosive applications. However, great care must be taken if junctions between metallic and non-metallic systems are inevitable. Non-metallic components and cemented junctions can be very intolerant of pulsating flow described previously. Electrical continuity must be ensured, anti-static precautions may be necessary. Some valves are designed for specific applications. Some can be modified to possess specific qualities, such as hygienic cleanliness or material compatibility for sour service. Valves must have ports which will make "pigging" practical. Very high local velocities can result in rapid wear and erosion ,so hard metals can be used for disks and seats or these valves


should only be used for isolation to avoid high velocities. Gate valves are selected for slow manual operation, resulting in no water hammer(surge) problems. Temperature changes, while the double-disk gate type design is closed, do not cause the gate to jam solid. This valve design is available in sizes from DN50 to DN600, 2" to 24" nb, with pressure ratings up to 100 barg on 600 Ib flanges. Body materials include steel, stainless steel, duplex stainless steel and nickel alloys to cope with a temperature range of-200 to 816o C . The bonnet can be extended to permit stem seal and actuator to be powered. All styles of wedge gate valves are prone to "chattering" when used for flow regulating or throttling, the wedge is loosely guided by cast passages in the body when not in full contact with the seats, both the wedge and seats can wear or be damaged by throttling. The diameter and unsupported length of the stem, plus the design of the wedge attachment to the stem, determine the valve's susceptibility to vibration. Wedge gate valves are recommended for isolation only .The upper portion of the valve body must be wide enough to accommodate the gate. This means the bonnet attachment can be almost elliptical. Some designs use circular bonnets which makes the valve body longer than strictly necessary but greatly improves the access to the internals. Bolted bonnets are standard on steel valves rated for 16 barg and over. Small brass and bronze valves, for up to 10 barg applications, will have screwed bonnets and integral seats. Carbon steel valves generally have screwed seats and some designs include "O" ring seals. Seat designs can be modified for fire-safe applications. Valve bodies can be partially lined by fitting long seat inserts through the connections. The location of the bonnet on the body is critical for the gate to be centrally placed between the


seats, if the gate is offset axially, the stem will be bent when the valve is closed, possibly leading to fatigue. A good, positive bonnet location is essential for long trouble-free operation; a spigot is probably best for low pressure valves, a ring-type joint performing a double function on high pressure valves. A spiral-wound gasket under the spigot is a good method of sealing low pressure bonnets. Large valves may have a clamped bonnet and so alignment is assured. The bonnet can be extended for cold and hot applications. Bottom of the packing box should be fitted with a backseat bush of reasonable length. This provides stem guidance and alignment. If it is too short, rapid wear can occur if the valve is operated often. The bottom of the stem should form a good seal with the backseat bush to allow repacking with the valve on-line. Both components may be described as "stainless steel" when they are made of 11/13 Cr, AISI 410. Ensure that corrosion will not be a problem or else the back seal will be ineffective when required. Small brass and bronze valves will have screwed glands. Steel valves are generally bolted. A form of graphite packing is the popular standard. Standard valves can have the packing box extended for vacuum applications. Most valves are of the outside screw, rising stem type. Depending upon the pressure rating, valves over DN200 may have geared handwheels; valves over DN350 will always have geared handwheels. Brass/bronze is popular for small low pressure water applications. Cast and forged carbon steel are popular for larger install -

lations . Valves with closed die – forged bodies may have

reduced ports . Some forged body valves have flanges

attached by butt welding or friction welding; check the quality

لعلم صدقة جاريه لروح من أعدهاللهم اجعل هذا ا (57)

assurance on the joint. Forged body valves can have welded

bonnets for increased integrity . The weld can be difficult to

inspect, so integrity may not be verified.

A few manufacturers make cast iron valves for PN16 ratings. These valves feature an inside screw/non-rising stem with gunmetal seats and gunmetal inserts in the cast iron wedge. Aimed at waterworks applications, the valves can operate between -100 C to 2200 C Table 3.2 indicates the sizes and ratings of some popular wedge gate valves.

Table 3.2 Popular wedge gate valves

(1)Bellows sealed packing box with butt weld connections option.

Because this valve is not sensitive for throttling action, it is not preferable for use in flow control. Furthermore, the high flow velocity during the throttling will cause erosion of the gate and seating surfaces, as well as the vibration of throttling process may result in chattering of the partially opened valve disc. But there are some valves are particularly designed for use in low-velocity throttling such as guillotine gate valves. There are two types of gate valves: rising stem valves fig (2) in which the valve position is very clear and non rising stem type fig (3) in which the vertical space is smaller. There are some disadvantages of gate valves that must be considered when selecting a gate valve for an application: -


Figure24: Gate Valve

It is not a quick opening or closing valve.

It is a large space valve.

It is not suitable for throttling applications. It is prone to vibration in the partially open state. It is more subject to seat and disk wear than a globe valve. Repairs, such as lapping and grinding, are generally more difficult to accomplish.

هذا العلم صدقة جاريه لروح من أعده اللهم اجعل (59)

1- Gate Valve Disk Design: Gate valves are available with a variety of disks. Classification of gate valves is usually made by the type disk used: solid wedge, flexible wedge, split wedge, or parallel disk. Solid wedges, flexible wedges, and split wedges are used in valves having inclined seats. Parallel disks are used in valves having parallel seats. Regardless of the style of wedge or disk used, the disk is usually replaceable. In services where solids or high velocity may cause rapid erosion of the seat or disk, these components should have a high surface hardness and should have replacement seats as well as disks. If the seats are not replaceable, seat damage requires removal of the valve from the line for refacing of the seat, or refacing of the seat in place. Valves being used in corrosion service should normally be specified with replaceable seats and the discs can be coated with an elastomer to improve sealing and reduce corrosion. Seat faces can be hard faced to reduce wear, corrosion, galling and friction. There are different types of disks as follows:-

1-1 Wedge Disk:

This disk has two tapered surfaces to get a firm contact between the side surface of the gate and the faced surface of the seat in the fully-closed position after tightening the stem. There are four types of wedges solid, hollow, split, and flexible wedge. 1-1-1 Solid-wedge disk :

It is a single piece solid construction, the alignment between

the disc surface is not affected by pipe-end loads or thermal fluctuations. It is the most economical gate, it is generally preferable for 2 inch diameters or smaller in lower pressure-


temperature applications (moderate applications). The solid wedge gate valve shown in Figure 25 is the most commonly used disk because of its simplicity and strength.

Figure 26: Flexible Wedge Figure 25: Solid Wedge

A valve with this type of wedge may be installed in any position and it is suitable for almost all fluids. It is practical for turbulent flow.

1-1-2 Flexible Wedge Disk: The flexible wedge gate valve illustrated in Figure 26 is a one-piece disk with a cut around the perimeter to improve the ability to match error or change in the angle between the seats. The cut varies in size, shape, and depth. A shallow, narrow cut gives little flexibility but retains strength.


A deeper and wider cut, or cast-in recess, leaves little material at the center, which allows more flexibility but compromises strength.

1-1-3 Hollow wedge : is one piece of a threaded hole in the center engaged with the

threaded stem, the hollow wedge travels along the stem

when it is rotated. In this case, the stem doesn’t go up and

down.

1-1-4 Split Wedge Disk: Split wedge gate valves, as shown in Figure 27, are of the ball and socket design. These are self-adjusting and self aligning to both seating surfaces. The disk is free to adjust itself to the seating surface if one-half of the disk is slightly out of alignment because of foreign matter lodged between the disk half and the seat ring. This type of wedge is suitable for handling non condensing gases and liquids at normal temperatures, particularly corrosive liquids. Freedom of movement of the disk in the carrier prevents binding even though the valve may have been closed Figure 27: Split Wedge when hot and later contracted due to cooling. This type of valve should be installed with the stem in the vertical position.

1-2 Double - Disk :

In this type the gate consists of two parallel discs move

against two parallel seats fig (28,29,30) the disks are forced


against the valves seats by a wedding mechanism when the

stem is tightened after the stroke is completed.

When the valve is closed and there is a pressure difference

between the two sides of the gate, acting at the lower

pressure side, causing a firm contact and high friction, then

the required torque needed to start opening will be higher,

but this problem is solved in this type because when the stem

tightening is released, the contact between the gate and the

seat is also released, then the disc is not jammed into the seat,

then it is easy to open the valve.

Fig 28: Double–Disk Rising Stem Flanged-End Fig 29 : Double-Disk Non Rising-

Gate Valve for 150-psig service Stem Gate Valve


This is particularly important when motors are used for opening and closing the valve - this type is favored for high - temperature steam ser-vice because it is less likely to stick in the closed position as a result of change in temperature.

Fig (30): Parallel-seat gate valve showing welded

construction for high-temperature service

with welded-in seat ring.

1-3 Conduit Disk:

In this type the gate is a long disk fig (31) consists of two parts,

the lower part has a circular hole of a same diameter of the

connecting pipe, but the upper part is solid. When the stem is

turned downward the solid part will go down to close the val-

ve passage and when it is turned upward the circular hole goes

up against the flow passage until the valve is completely open.

This valve is used in pipelines where pigs are run through the


piping for inspection or cleaning or as a barrier between the

different oil products. The valve requires a large space

envelope because of its longer disc.

Fig 31: Conduit Disk Valve

1-4 Parallel Disk: The parallel disk gate valve illustrated in Figure 32 is designed to prevent valve binding due to thermal transients. This design is used in both low and high pressure applications. The wedge surfaces between the parallel face disk halves are caused to press together under stem thrust and spread apart the disks to seal against the seats. The tapered wedges may be part of the disk halves or they may be separate elements. The lower wedge may bottom out on a rib at the valve bottom so that the stem can develop seating force. In one version, the wedge contact surfaces are curved to keep the point of contact close to the optimum.


In other parallel disk gates, the two halves do not move apart under wedge action. Instead, the upstream pressure holds the downstream disk against the seat. A carrier ring lifts the disks, and a spring or springs hold the disks apart and seated when there is no upstream pressure.

Figure 32: Parallel Disk

Another parallel gate disk design provides for sealing only one port. In these designs, the high pressure side pushes the disk open (relieving the disk) on the high pressure side, but forces


the disk closed on the low pressure side. With such designs, the amount of seat leakage tends to decrease as differential pressure across the seat increases. These valves will usually have a flow direction marking which will show which side is the high pressure (relieving) side. Care should be taken to ensure that these valves are not installed backwards in the system.

2 - Gate Valve Stem Design: Gate valves are classified as either rising stem or nonrising stem valves. For the nonrising stem gate valve, the stem is threaded on the lower end into the gate. As the hand wheel on the stem is rotated, the gate travels up or down the stem on the threads while the stem remains vertically stationary. This type valve will almost always have a pointer-type indicator threaded onto the upper end of the stem to indicate valve position. Figures 2 and 3 illustrate rising-stem gate valves and nonrising stem gate valves. The nonrising stem configuration places the stem threads within the boundary established by the valve packing out of contact with the environment. This configuration assures that the stem merely rotates in the packing without much danger of carrying dirt into the packing from outside to inside. Rising stem gate valves are designed so that the stem is raised out of the flow path when the valve is open. Rising stem gate valves come in two basic designs. Some have a stem that rises through the handwheel while others have a stem that is threaded to the bonnet.

3 - Gate Valve Seat Design: Seats for gate valves are either provided integral with the valve body or in a seat ring type of construction. Seat ring construction provides seats which are either threaded into position or are pressed into position and seal welded to the valve body. The latter form of construction is recommended for higher temperature service.


Integral seats provide a seat of the same material of construction as the valve body while the pressed-in or threaded-in seats permit variation. Rings with hard facings may be supplied for the application where they are required. Small, forged steel, gate valves may have hard faced seats pressed into the body. In some series, this type of valve in sizes from 1/2 to 2 inches is rated for 2500 psig steam service. In large gate valves, disks are often of the solid wedge type with seat rings threaded in, welded in, or pressed in. Screwed in seat rings are considered replaceable since they may be removed and new seat rings installed.

=========================================== (1-2-5-2) Globe Valves: Globe valve is a linear motion valve used to stop, start, and regulate fluid flow. Its name is taken from the shape of its body and sometimes its disk. This valve is classified according to the relative position of its ports, if they have one straight centerline , the valve is called Straight Globe Valve or ( in-line valve ) Fig 33, the flow path inside the valve is not straight the flow must change direction in straight valve through 90o in order to pass through the seat and then another 90o to return to the original direction, This path increases the pressure losses (drop) through the valve more than in gate valve . Brass and bronze valves, with screwed bonnets/glands and connections, suitable for 10 barg are used extensively for clean water applications. Popular cast and forged steel straight globe valve ranges are listed in Table 6 If the centerline for each port is perpendicular to the other it is called Angle Globe Valve Fig 33 , the flow must change direction 90o in angle globe valve. Flow always enters under the seat. The flow path is much more open and less tortuous


than the straight version with consequently less pressure drop. The valve body will be subjected to fluid reaction forces due to the change in flow direction.These forces will normally be insignificant but as valve size and fluid density increase, the

Angle Globe Valve Straight Globe Valve

Fig 33: Globe Valve

magnitude of the forces should be taken in consideration.

Small screwed valves in brass and bronze are used extensively in clean water applications Larger high pressure angle globe valves, or choke valves, are used for continuous throttling in crude oil and natural gas production. but with high operating pressures and operating conditions deteriorate the valve due to sand, H2S and CO2 content. Solids erosion combined with cavitation erosion produced rapid material loss requiring frequent valve adjustment. In globe valves the disc should be attached to the stem with a self-aligning connection so that closing forces are applied to


the seat evenly. The disc does not rotate against the seat and there are no galling tendencies between similar materials. Table 6 : Popular cast and forged steel straight globe valve sizes and ratings

(1) Welded bonnet (2) Extended cooled bonnet for 800~ operation The essential principle of globe valve operation is the perpendicular movement of the disk away from the seat, this causes the annular space between the disk and seat ring to gradually close as the valve is closed. This characteristic gives the globe valve good throttling ability, which permits its use in regulating flow. Therefore, the globe valve may be used for both stopping and starting fluid flow and for regulating flow. When compared to a gate valve, a globe valve generally yields much less seat leakage. This is because the disk movement to the contact surface of the seat is at a right angle, which permits the force of closing close the disk to tightly to the seat. Globe valves can be arranged so that the disk closes against or in the same direction of fluid flow. When the disk closes


against the direction of flow, the kinetic energy of the fluid impedes closing but aids opening of the valve. When the disk closes in the same direction of flow, the kinetic energy of the fluid aids closing but impedes opening. This characteristic is preferable to other designs when quick-acting stop valves are necessary. Globe valves also have drawbacks. The most evident shortcoming of the simple globe valve is the high head loss from two or more right angle turns of flowing fluid. Obstructions and discontinuities in the flow path lead to head loss. In a large high pressure line, the fluid dynamic effects from pulsations, impacts, and pressure drops can damage trim, stem packing, and actuators. In addition, large valve sizes require considerable power to operate and are especially noisy in high pressure applications. Other drawbacks of globe valves are the large openings necessary for disk assembly, heavier weight than other valves of the same flow rating, and the hanging mounting of the disk to the stem.

(1-2-5-2-1) Globe Valve Design: 1- Globe Valve Body Designs: Bodies are normally cast or die-forged in one piece Duplex stainless steel valves are available for special applications. One-piece body valves may have integral seats. Valves for high pressure throttling may have the seating surface hard-faced to extend their useful life. Seats can be machined, lapped and polished in situ and integral seats can be useful in applications where crevice corrosion is a problem. There are four primary body designs for globe valves are Z-body, Y-body, Angle, and double- beat. . 1-1 Z-Body Design: The simplest design and most common for water applications is the Z-body. The Z-body is illustrated in Figure 34 . For this body design, the Z-shaped diaphragm or partition across the


globular body contains the seat. The horizontal setting of the seat allows the stem and disk to travel at right angles to the pipe axis. The stem passes through the bonnet which is attached to a large opening at the top of the valve body. This provides a symmetrical form that simplifies manufacture, installation, and repair.

Fig 34: Z- Body Globe Valve

1-2 Y-Body Design: By setting the stem and seat at an angle to the body the flow path is straightened somewhat and the flow losses reduced. The oblique style is more popular for general applications than the angled, which is largely used for steam. Flow is in


Figure 35: Y-Body Globe Valve

one direction. Full-bore and reduced port versions Figure 35 illustrates a typical Y-body globe valve with screwed bonnet. This design is a remedy for the high pressure drop inherent in Z-Body globe valves. The seat and stem are angled at approximately 45°. The angle yields a straighter flow path (at full opening) and provides the stem, bonnet, and packing a relatively pressure resistant envelope. Y-body globe valves are best suited for high pressure and other severe services. In small sizes for intermittent flows, the pressure loss may not be as important as the other considerations favoring the Y-body design . High pressure valves, with integral bonnet in closed die-forged high tensile


steel, and bolted gland, can operate at high temperatures. Table 7 indicates typical performance of the pressure ratings available. Table 7 : High pressure/temperature oblique globe valve performance

1-3 Angle Valve Design: The angle body globe valve design, illustrated in Figure36 , is a simple modification of the basic globe valve. Having ports at right angles. A particular advantage of the angle body design is that it can function as both a valve and a piping elbow. Most bodies for industrial use are made in cast steel with bolted bonnets. Bronze, stainless steel and duplex materials are readily available. For moderate conditions of pressure, temperature, and flow, the angle valve closely resembles the ordinary globe. The angle valve's discharge conditions are favorable with respect to fluid dynamics and erosion.

العلم صدقة جاريه لروح من أعده اللهم اجعل هذا (74)

Figure 36 : Angle Globe Valve

1-4 Double-Beat Body Design: The double-beat globe valve is an old design which is very useful for special applications. Figure 37 shows the basic construction of its body. Globe valves are very good for low leakage shut-off and regulation. As the valve size and the operating pressure increase, the hydraulic load on the stem becomes greater making the valve difficult to operate manually. This problem was first experienced with steam engines as sizes and steam pressures increased to produce more power. The double-beat globe valve reduces the hydraulic load by balancing the forces on the discs. The upper disc has inlet pressure on the top; the lower disc has


inlet pressure on the bottom. The areas are not quite equal, because of the difference between the inner and outer seat diameters, this difference is very small and produces only a small thrust for large high pressure valves. Operation by ungeared handwheel with rising stem valves can be considered for applications impossible with other valves. They are also very good for use on sites without power or for emergency back-up systems.

Figure 37: A double-beat globe valve

As with other globe valves there is some flow resistance, but this may not be as high because two seats are used. Double- beat globe valves cannot be cleaned with rods or "pigged". Operation with clean fluids is preferred to reduce the possibility of differential seat/disc wear. Essentially the valve has two pressure casings. The outer casing being at inlet pressure and the inner at outlet pressure. The incoming flow circulates around the casing and flows through both seats into the inner casing. Flow in either


direction is possible; sealing in both directions is equal. The discs require a degree of flexibility to ensure both seat properly. The body is relatively complicated and casting is the preferred method of construction. However fabrication and forging is possible if necessary. Connections (ports) do not necessarily have to be in-line. They can be at 90o without significantly affecting the flow losses, so it can be manufactured as straight or angle globe valve Double-beat globe valves are reserved for special applications and probably made to order. Typical applications include main isolating valves for steam and water turbines.

2- Globe Valve Disks Design: Most globe valves use one of three basic disk designs: the ball disk, the composition disk, and the plug disk.

2-1 Ball (Globe) Disk: The ball disk fits on a tapered, flat-surfaced seat. The ball disk design is used primarily in relatively low pressure and low temperature systems. It is capable of throttling flow, but is primarily used to stop and start flow.

2-2 Composition Disk: The composition disk design uses a hard, nonmetallic insert ring on the disk. The insert ring creates a tighter closure. Composition disks are primarily used in steam and hot water applications. They resist erosion and are sufficiently resilient to close on solid particles without damaging the valve. Composition disks are replaceable.

2-3 Plug Disk: Because of its configuration, the plug disk provides better throttling than ball or composition designs. Plug disks are available in a variety of specific configurations. In general, they are all long and tapered.

3- Globe Valve Disk and Stem Connections Design: Globe valves employ two methods for connecting disk and stem:


T-slot construction and disk nut construction: In the T-slot design, the disk slips over the stem. In the disk nut design, the disk is screwed into the stem.

4- Globe Valve Seats Design: Globe valve seats are either integral with or screwed into the valve body. Many globe valves have backseats. A backseat is a seating arrangement that provides a seal between the stem and bonnet. When the valve is fully open, the disk seats against the backseat. The backseat design prevents system pressure from building against the valve packing.

(1-2-5-2-2)Globe Valve Direction of Flow: For low temperature applications, globe and angle valves are ordinarily installed so that pressure is under the disk. This promotes easy operation, helps protect the packing, and eliminates a certain amount of erosive action to the seat and disk faces. For high temperature steam service, globe valves are installed so that pressure is above the disk. Otherwise, the stem will contract upon cooling and tend to lift the disk off the seat.

(1-2-5-2-3) Advantages of Globe valves:

- Good for throttling capability. - Shorter stroke than gate valves. - Easy to machine or resurface the seats. - It can be used as a stop-check valve. - Good shutoff for ordinary sizes because the disk-to-seat ring contact is more at right angles, which permits the . force of closing to tightly seat the disk.

(1-2-5-2-4) Disadvantages:

- Higher pressure drop than gate valves - Require greater torque to close the valve. - Higher rate of erosion in the closure element - In a large high pressure line, the fluid dynamic


effects from pulsations, impacts, and pressure drops can damage trim, stem packing, and actuators. - large valve sizes are especially noisy in high pressure applications. -Other drawbacks of globe valves are the large openings necessary for disk assembly, heavier weight than other valves of the same flow rating, and the cantilevered mounting of the disk to the stem.

(1-2-5-2-5) Applications: The typical applications of this valve are as follows :-

- The applications in which the flow needs to be regulated and

leak tightened such as systems of fuel oil, lubricating oil,

cooling water, steam, chemical feeding.

-The applications of very slight flow such as venting and . drainage in high pressure lines ====================================================

(1-2-5-3) Ball Valves: A ball valve is a rotational motion valve that uses a ball-shaped disk to stop or start fluid flow Fig 38 , 39 The ball, shown in Figure 40, performs the same function as the disk in the globe valve. When the valve handle is turned to open the valve, the ball rotates to a point where the hole through the ball is in line with the valve body inlet and outlet. When the valve is shut, the ball is rotated so that the hole is perpendicular to the flow openings of the valve body and the flow is stopped. Most ball valve actuators are of the quick-acting type, which require a 90° turn of the valve handle to operate the valve. Other ball valve actuators are planetary gear-operated to increase the operating time to avoid hammering (surge). This type of gearing also allows the use of a relatively small handwheel and operating force to operate a fairly large valve.


Fig : 38

Fig: 39


Figure 40 : Typical Ball Valve Theory

The ball valve can have very low fluid resistance and very high Cv values consequently. These properties depend upon the size of the port through the ball. Most ball valve designs can be both full-bore(same diameter as the piping) and reduced bore. Ball valves should be used as isolating valves and not for throttling. The ball and seat materials must be compatible for rubbing contact with ball surface under pressure, the rubbing velocity between them is low but the interface pressure can be very high. Self-lubricating materials, such as PTFE, are popular for seats for a wide range of applications. Designs with metal balls and metal seats can be used for applications with solids


handling. Valves with metal seats are more costly than soft seat valves but they are expected to last at least twice as long.

(1-2-5-3-1) Advantages: A ball valve is generally the least expensive of any valve configuration and has low maintenance costs. In addition to quick, quarter turn on-off operation, ball valves are compact, require no lubrication, and give tight sealing with low torque.

(1-2-5-3-2) Disadvantages: Conventional ball valves have relatively poor throttling characteristics. In a throttling position, the partially exposed seat rapidly erodes because of the impingement of high velocity flow.

(1-2-5-3-3) Valve Parts Design: 1- Port Patterns Design: Ball valves are available in the venturi, reduced, and full port pattern. The full port pattern has a ball with a bore equal to the inside diameter of the pipe.

2- Body Design: Ball valve body may be made as one piece or two or three pieces from different materials table 8 in wide range of valve size, ball bore size, and rated pressure table 9.

2-1 One-piece body ball valve: The one-piece body ball valve is an inherently high integrity valve. The number of leak paths to atmosphere is reduced to minimum. Standard valves have a single body casting which can include the bonnet. Small valves with screwed connections can be machined from barstock.


Table 8 : Three-piece body ball valve materials

Table 9 :Sizes and pressures of popular ball valves

(1) Union construction with PVC, PP or PVDF bodies and balls

Special purpose high integrity valves can be manufactured by machining from a solid forging, internal access being gained through the bonnet and bottom flange when fitted. One-piece body valves are available in a wide range of sizes and materials. Popular reduced bore valves, suitable for pressures of 20 barg or 50 barg, are available from 1/2". These can be cast in ductile iron, steel, stainless steel, MonelTM, Alloy 20 and aluminium bronze. Special one-piece


ball valves, with integral metal seats, are suitable for cryogenic applications and hot services to more than 1100oC with operating pressures from vacuum to over 3000 barg. The metal seats make these valves suitable for solidshandling applications. Standard valves are assembled through one of the end connections, as shown in Figure 41.

Fig 41 :One-piece body cast ball valve

The body casting is not symmetrical. Although the flange connections are identical in size the body passage from one flange is larger. A seat is fitted into its location first, then the spindle is fitted through the bore. Special valves are machined from solid forgings. The bore for the bonnet must be large enough to pass the ball. Connections can be machined directly on the end of the forging or added by welding.

2-2 Two-piece body ball valve:

Small barstock valves for instrument and allied applications (84) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

can be made using the two-piece body construction. One seat is inserted down the bore of the body. Then the spindle is fitted up through the body into the integral bonnet. The ball must slide into the body and engage the tongue on the spindle. The second seat is fitted. The end of the body is closed by a screwed union which forms the other process connection. These valves, in sizes from 1/8" to 1/2" NPT, can be capable of 414 or 690 barg. Small valves in ductile iron or brass, 1/4" to 2", with PTFE seats and seals can operate between -20oC and 160o C with pressures up to 64 barg. Similar valves in cast steel are suitable for-40oC to 230oC at pressures up to 100 barg. A restricted size range, 6" to 10", is offered in a wide range of body and seat materials. Bodies are cast in: * Ductile iron, carbon steel, aluminium, bronze * Aluminium bronze, Monel TM, stainless steel, Alloy 20. The reduced-bore valves with integral bonnet and gland are suitable for ANSI 1501b and 3001b pressure ratings and operating temperatures can span -200o C to 370o C with metallic and non-metallic seats. All valves except aluminium bronze can be fire-safe. Stainless steel full-bore valves are mass-produced in sizes from DN25 to DN600 in pressure ratings of PN10, 16, 25 and 40. Bolted bonnet and gland are standard with PTFE packing. Temperature range is -50o C to 230o C. Metal seats are an option. Carbon steel versions up to DN300 can have a temperature range of-200o C to 450o C Valves split around the spindle centre-line are produced in steel and stainless steel from 2" to 36". Pressure ratings cover ANSI 1501b, 3001b and 600lb. Various seat and seal options can be fitted, including metallic and graphite, which cover operating temperatures from -200o C to 600o C. Two-piece body valves are available in both full-bore and reduced-bore styles.These can be fully lined with an elastomer


for corrosion protection. FEP, PFA and UHMWPE are popular compounds. Lined valves are mass-produced in sizes from DN25 to DN150 for cold working pressures up to 19 barg. Figure 35 shows a full-bore ball valve with integral bonnet and spring-loaded chevron packing.

2-3 Three-piece body ball valve: Three-piece body ball valves can be both full-bore and reduced - bore and specifications must be examined in detail to check the ball bore . The three - piece body construction is very versatile and allows many variations in detail design. An ideal method for the manufacture of large valves (over DN1 000 is claimed by some companies), but this method can also be suitable for small valves. The basic design concept is a ball mounted in a central portion, Fig 40 with two identical end connectors clamping the seats in position. These valves are suitable for liquids and gases. A seat is placed in each end of the body and the end pieces bolted up. The seats locate the ball in the body. Sealing is accomplished by fluid forces moving the ball slightly towards the downstream seat. Metal valves can be lined with non-metallic materials for corrosion resistance. FEP, PFA and UHMWPE are popular choices.These materials exhibit the chemical resistance of PTFE butpossess superior moulding qualities.The lining can be separateand replaceable or actually moulded to the valve body.With the latter the lining is attached by plain or dovetail grooves. In some designs the lining extends through the packing box. The generation of static electricity can be a problem and a complete electric circuit must be ensured to avoid arcing.

3- Ball Design: Balls are usually metallic in metallic bodies with trim (seats) produced from elastomeric (elastic materials resembling


rubber) materials. Table 3.11 lists different materials can be used in ball design. Plastic construction is also available. . The trunnion-mounted ball valve has two journal bearings to locate the ball within the body. Trunnion-mounted ball valves are intended to seal equally in both directions.

4- Seat Design: Some ball valves only have one seat and will only seal in one direction, these valves will have an arrow indicating the direction of flow. If sealing in both directions is essential this must be specified as a requirement to avoid costly surprises later the ball is being located by the seats. A seat is placed in each end of the body and the end pieces bolted up. The seats locate the ball in the body, sealing is accomplished by fluid forces moving the ball slightly towards the downstream seat. Temperature ranges for soft seats are -50o C to 230o C. Various seat and seal options can be fitted, including metallic and graphite, which cover operating temperatures from -200o C to 600o C. The resilient seats for ball valves are made from various elastomeric material. The most common seat materials are teflon (TFE), filled TFE, Nylon, Buna-N, Neoprene, and combinations of these materials. Because of the elastomeric materials, these valves cannot be used at elevated temperatures. Care must be used in the selection of the seat material to ensure that it is compatible with the materials being handled by the valve.

5- Ball Valve Stem Design: The stem in a ball valve is not fastened to the ball. It normally has a rectangular portion at the ball end which fits into a slot cut into the ball.


The enlargement permits rotation of the ball as the stem is turned.

6- Seal (Packing) Design: Packing for ball valve stems is usually in the configuration of die-formed packing rings normally of TFE, TFE-filled, or TFE-impregnated material. Some ball valve stems are sealed by means of O-rings rather than packing. Some designs have pressure energised packing and no gland.

7- Ball Valve Bonnet Design: A bonnet cap fastens to the body, which holds the stem assembly and ball in place. Adjustment of the bonnet cap permits compression of the packing, which supplies the stem seal.

(1-2-5-3-4) Ball Valve Position: Some ball valves are equipped with stops that permit only 90° rotation. Others do not have stops and may be rotated 360°. With or without stops, a 90° rotation is all that is required for closing or opening a ball valve. The handle indicates valve ball position. When the handle lies along the axis of the valve, the valve is open. When the handle lies 90° across the axis of the valve, the valve is closed. Some ball valve stems have a groove cut in the top face of the stem that shows the flowpath through the ball. Observation of the groove position indicates the position of the port through the ball. This feature is particularly advantageous on multiport ball valves.

============================================ (1-2-5-4) Plug Valves A plug valve is a rotational motion valve used to stop or start fluid flow. The name is derived from the shape of the disk, which resembles a plug The simplest form of a plug valve is


the pet cock Fig 42 . The body of a plug valve is machined to receive the tapered or cylindrical plug. The disk is a solid plug

Fig 42:Small parallel plug valve with "0" ring seals

With a bored passage at a right angle to the longitudinal axis of the plug. . Plug valves are available in either a lubricated or non lubricated design and with a variety of styles of port openings through the plug as well as a number of plug designs. Valves are made in various materials to suit a wide range of applications, see Table 10. Popular valve sizes are from DN 15 to DN200 with pressure ratings from PN10 to


PN40. Valves up to 6" can be ANSI 300lb. Valves up to 18" nb are produced regularly with pressure ratings up to ANSI 300lb. Valves over DN100 will have a geared handwheel. The temperature range is largely controlled by the seat material, see Table 11

Table 10 : Materials for tapered plug valves

Table11 : Taper plug valve seat material temperature range

(1-2-5-4-1) Plug Valve Design: 1- Plug Design: Two shapes of plugs are being used in plug valves as follows:-

1-2 Parallel Plug Design: The basic valve has a solid plug rotating in a close fitting cylindrical body. When direct metal-to-metal contact is used for sealing, considerable torque may be required to operate the valve. Coatings may be applied to the body and/or the plug to reduce friction and improve sealing. Typical coatings include PTFE, Rislan TM and ceramics. Plugs may be hard faced to reduce wear and galling tendencies. A complete PTFE sleeve


can be fitted between the plug and the body to seal and lubricate, the sleeve can easily be replaced when worn, valves without sleeves should have much harder bodies than plugs; the plug can be replaced when worn. No adjustment for wear is possible, and parts replacement is inevitable.

Figure 43: Plug valve with three-piece wedge plug

The plug can be fitted with a top "O" ring to eliminate the need for a packing box. The bore for the plug is machined straight through the body, see Figure 42. The plug is made in the same material as the body and is coated with PTFE and is fitted with "O" rings around the port to assist sealing and top


and bottom around the plug. No bonnet is fitted. The standard "O" rings are PTFE coated VitonTM. The plug is located by a circlip on the bottom and the operating lever on the top. Operating pressure is up to 207 barg at temperatures between -23o and 204o C. A silicone- based grease lubricant, supplied by the manufacturer, is recommended for good service life. Larger flanged valves in cast steel, with a PTFE sleeve, are suitable for 50 barg at temperatures up to 200o C. Another design variation in parallel plug is one in which the plug consists of three pieces, see Figure 43. The central portion, attached to the spindle, has a shaped port. Full bore and reduced bore versions are also available. The two faces at right angles to the port are tapered and carry separate shoes which together form a parallel sealing shell. When open, the spindle is raised, reducing the outside diameter of the loose shoes, allowing the spindle to rotate without the shoe peripheries contacting the valve body. The top and bottom edges of the shoes are constrained by the bonnet and bottom flange. To close, the plug first rotates 90o and presents the two loose shoes to the process connections. The spindle and central portion then descend and expand the outside diameter of the sealing shoes. The sealing shoes are wedged against the process ports. The ports are wedged closed against each other to form a very rigid mechanical system. The loose shoes may be fitted with elastomer or graphite seals to reduce leakage rates. The spindle is guided in bearings in both the bonnet and bottom flange to ensure the loose shoes are always clear of the body ports when rotation occurs. The shoes can be removed through the bottom flange, for inspection or replacement, without disturbing the rest of the valve. As both process ports are sealed independently these valves can be used for double block and bleed applications.


Table 12 : Sizes and ratings of three-piece wedge plug valves

Generally, the plug is made in carbon steel or low. They are made in a range of sizes and ratings, Table 12. A special version is also available which enables the shoes to be changed without draining the pipeline. These valves can be certified as fire-safe. All sizes can be fitted with geared handwheels to eliminate water hammer problems. This valve has the capability of having very low fluid resistance and high Cv values. This is dependent upon the port shape and size.

1-3 Tapered Plug Design: The tapered plug is a derivative of the parallel plug . Slight wear of the surface of the plug can be accommodated by lowering the plug in the body.

Figure 44 : Tapered plug valve with integral gland


The position of the plug is usually adjusted automatically by spring-loading. Tapered plug can be full-bore or reduced bore. The port area of reduced port valves may only be 50% of the nominal pipe size. Also the port may not be circular. The plug may not touch the body casting internally and may be completely supported by the seats. The wiping action of the plug against the seats may help to keep the seats clean. If the bonnet and gland are integrated and spring-loaded packing is used, one spring stack can perform both functions, see Figure 44 ..The gland can be loaded by external springs and used to ensure good plug contact with the liner. PTFE and PFA are popular liner materials..

2- Plug Ports Design: An important characteristic of the plug valve is its easy adaptation to multiport construction. Multiport valves are widely used. Their installation simplifies piping, and they provide a more convenient operation than multiple gate valves. They also eliminate pipe fittings. The use of a multiport valve, depending upon the number of ports in the plug valve, eliminates the need of as many as four conventional shutoff valves. Plug valves are normally used in non-throttling, on-off operations, particularly where frequent operation of the valve is necessary. These valves are not normally recommended for throttling service because, like the gate valve, a high percentage of flow change occurs near shutoff at high velocity. However, a diamond-shaped port has been developed for throttling service.

2-1 Rectangular Port Plug Design: The most common port shape is the rectangular port. The rectangular port represents at least 70% of the corresponding pipe's cross-sectional area


2-2 Round Port Plug Design: Round port plug is a term that describes a valve that has a round opening through the plug. If the port is the same size or larger than the pipe's inside diameter, it is referred to as a full port. If the opening is smaller than the pipe's inside diameter, the port is referred to as a standard round port. Valves having standard round ports are used only where restriction of flow is unimportant.

2-3 Diamond Port Plug Design: A diamond port plug has a diamond-shaped port through the plug. This design is for throttling service. All diamond port valves are venturi restricted flow type.

3- Plug Valve Glands Design: The gland of the plug valve is equivalent to the bonnet of a gate or globe valve. The gland secures the stem assembly to the valve body. There are three general types of glands: single gland, screwed gland, and bolted gland. To ensure a tight valve, the plug must be seated at all times. Gland adjustment should be kept tight enough to prevent the plug from becoming unseated and exposing the seating surfaces to the live fluid. Care should be exercised to not overtighten the gland, which will result in a metal-to-metal contact between the body and the plug. Such a metal-to-metal contact creates an additional force which will require extreme effort to operate the valve.

(1-2-5-4-2) Plug Valve Theory: In the open position Fig 45, the passage in the plug lines up with the inlet and outlet ports of the valve body. When the plug is turned 90° from the open position, the solid part of the plug blocks the ports and stops fluid flow.


Figure 45: Plug Valve Theory

(1-2-5-4-3) Multiport Plug Valves: Multiport valves are particularly advantageous on transfer lines and for diverting services. A single multiport valve may be installed in lieu of three or four gate valves or other types of shutoff valve. A disadvantage is that many multiport valve configurations do not completely shut off flow. In most cases, one flow path is always open. These valves are intended to divert the flow of one line while shutting off flow from the other lines. If complete shutoff of flow is a requirement , it is necessary that a style of multiport valve be used that permits this, or a secondary valve should be


installed on the main line ahead of the multiport valve to permit complete shutoff of flow. In some multiport configurations, simultaneous flow to more than one port is also possible. Great care should be taken in specifying the particular port arrangement required to guarantee that proper operation will be possible.

(1-2-5-4-4) Lubricated Plug Valve Design: Clearances and leakage are the chief considerations in plug valves. Many plug valves are of all metal construction. In these versions, the narrow gap around the plug can allow leakage. If the gap is reduced by sinking the taper plug deeper into the body, actuation torque climbs rapidly and galling can occur. To remedy this condition, a series of grooves around the body and plug port openings is supplied with grease prior to actuation. Applying grease lubricates the plug motion and seals the gap between plug and body. Grease injected into a fitting at the top of the stem travels down through a check valve in the passageway, past the plug top to the grooves on the plug, and down to a well below the plug. The lubricant must be compatible with the temperature and nature of the fluid. All manufacturers of lubricated plug valves have developed a series of lubricants that are compatible with a wide range of media. Their recommendation should be followed as to which lubricant is best suited for the service. The most common fluids controlled by plug valves are gases and liquid hydrocarbons. Some water lines have these valves, provided that lubricant contamination is not a serious danger. Lubricated plug valves may be as large as 24 inches and have pressure capabilities up to 6000 psig. Steel or iron bodies are available. The plug can be cylindrical or tapered.

(1-2-5-4-5) Nonlubricated Plugs Design: There are two basic types of nonlubricated plug valves: lift-


type and elastomer sleeve or plug-coated. Lift-type valves provide a means of mechanically lifting the tapered plug slightly to disengage it from the seating surface to permit easy rotation. The mechanical lifting can be accomplished with a cam or external lever. In a common, nonlubricated, plug valve having an elastomer sleeve, a sleeve of TFE completely surrounds the plug. It is retained and locked in place by a metal body. This design results in a primary seal being maintained between the sleeve and the plug at all times regardless of position. The TFE sleeve is durable and inert to all but a few rarely encountered chemicals. It also has a low coefficient of friction and is, therefore, self-lubricating.

(1-2-5-4-6) Manually Operated Plug Valve Installation: When installing plug valves, care should be taken to allow room for the operation of the handle, lever, or wrench. The manual operator is usually longer than the valve, and it rotates to a position parallel to the pipe from a position 90° to the pipe.

=========================================== (1-2-5-5) Diaphragm Valves: A diaphragm valve is a linear motion valve that is used to start, regulate, and stop fluid flow. The name is derived from its flexible disk, which mates with a seat located in the open area at the top of the valve body to form a seal. A diaphragm valve is illustrated in Figure 46. Diaphragm valves are, in effect, simple "pinch clamp" valves. A resilient, flexible diaphragm is connected to a compressor by a stud molded into the diaphragm. The compressor is moved up and down by the valve stem. Hence, the diaphragm lifts when the compressor is raised.


Open Throttling Closed

Figure 46: Straight Through Diaphragm Valve

As the compressor is lowered, the diaphragm is pressed against the contoured bottom in the straight through valve type illustrated in Figure 46 or the body weir in the weir-type valve type illustrated in Figure 47. Diaphragm valves can also be used for throttling service. The weir-type is the better throttling valve but has a limite range. Its throttling characteristics are essentially those of a quick opening valve because of the large shutoff area along the seat. A weir-type diaphragm valve is available to control small flows. It uses a two - piece compressor component. Instead of the entire diaphragm lifting off the weir when the valve is opened, the first increments of stem travel raise an inner compressor component that causes only the central part of the diaphragm to lift. This creates a relatively small opening through the center of the valve. After the inner compressor is completely open, the outer compressor component is raised along with the inner compressor and the remainder of the throttling is similar to the throttling that takes place in a conventional valve. Diaphragm valves are particularly suited for the handling of corrosive fluids, fibrous slurries, radioactive fluids, or other fluids that must remain free from contamination.


Open Throttling Closed Figure47 : Weir Diaphragm Valve

(1-2-5-5-1) Diaphragm Construction: The operating mechanism of a diaphragm valve is not exposed to the media that flows in the pipeline.


Sticky or viscous fluids cannot get into the bonnet to interfere with the operating mechanism. Many fluids that would clog, corrode, or gum up the working parts of most other types of valves will pass through a diaphragm valve without causing problems. Conversely, lubricants used for the operating mechanism cannot be allowed to contaminate the fluid being handled. There are no packing glands to maintain and no possibility of stem leakage. There is a wide choice of available diaphragm materials depending on flow temperature, table 13 lists the temperature range for most popular diaphragm materials . Diaphragm life depends upon the nature of the material handled, temperature, pressure, and frequency of operation. Some elastomeric diaphragm materials may be unique in their excellent resistance to certain chemicals at high temperatures.

Table 13 : Diaphragm materials for weir type valves

(1) Specially processed PTFE to reduce entrained air and permeability and increase dimensional stability However, the mechanical properties of any elastomeric material will be lowered at the higher temperature with possible destruction of the diaphragm at high pressure.


However, the valve is specified by size, maximum and minimum pressure and temperature. Allowable maximum pressure for diaphragm valves is at the lower limit of temperature and is the minimum at maximum temperature Table 14.

Table 14 : Weir type diaphragm valve pressure/temperature limits

Consequently, the manufacturer should be consulted when valves are used in elevated temperature applications. All elastomeric materials operate best below 150°F. Some will function at higher temperatures. Viton, for example, is noted for its excellent chemical resistance and stability at high temperatures. However, when fabricated into a diaphragm, Viton is subject to lowered tensile strength just as any other elastomeric material would be at elevated temperatures. Fabric bonding strength is also lowered at elevated temperatures, and in the case of Viton, temperatures may be reached where the bond strength could become critical. Fluid concentrations is also a consideration for diaphragm selection. Many of diaphragm materials exhibit satisfactory corrosion resistance to certain corrodents up to a specific concentration and/or temperature. The elastomer may also have a maximum temperature limitation based on mechanical properties which could be in excess of the allowable operating temperature depending upon its corrosion resistance. This should be checked from a corrosion table.


(1-2-5-5-2) Diaphragm Valve Stem Assemblies: Diaphragm valves have stems that do not rotate. The valves are available with indicating and nonindicating stems. The indicating stem valve is identical to the nonindicating stem valve except that a longer stem is provided to extend up through the handwheel. For the nonindicating stem design, the handwheel rotates a stem bushing that engages the stem threads and moves the stem up and down. As the stem moves, so does the compressor that is pinned to the stem. The diaphragm, in turn, is secured to the compressor.

(1-2-5-5-3) Diaphragm Valve Bonnet Assemblies: Some diaphragm valves use a quick-opening bonnet and lever operator. This bonnet is interchangeable with the standard bonnet on conventional weir-type bodies. A 90° turn of the lever moves the diaphragm from full open to full closed. Diaphragm valves may also be equipped with chain wheel operators, extended stems, bevel gear operators, air operators, and hydraulic operators. Many diaphragm valves are used in vacuum service. Standard bonnet construction can be employed in vacuum service through 4 inches in size. On valves 4 inches and larger, a sealed, evacuated, bonnet should be employed. This is recommended to guard against premature diaphragm failure. Sealed bonnets are supplied with a seal bushing on the nonindicating types and a seal bushing plus O-ring on the indicating types. Construction of the bonnet assembly of a diaphragm valve is illustrated in Figure 47. This design is recommended for valves that are handling dangerous liquids and gases. In the event of a diaphragm failure, the hazardous materials will not be released to the atmosphere. If the materials being handled are extremely hazardous, it is recommended that a means be provided to permit a safe disposal of the corrodents from the bonnet.


(1-2-5-6) Pinch Valves: The relatively inexpensive pinch valve, illustrated in Figure 48, is the simplest in any valve design. It is simply consists of a sleeve molded of rubber or other synthetic material passing between two jowls of a pinching mechanism. the upper jowl is movable to pinch the flow. Pinch valves are suitable for on-off and throttling services. However, the effective throttling range is usually between 10% and 95% of the rated flow capacity.Pinch valves are ideally suited for the handling of slurries, liquids with large amounts of suspended solids, and systems that convey solids pneumatically. Because the operating mechanism is completely isolated from the fluid, these valves also find application where corrosion or metal contamination of the fluid might be a problem. All of the operating portions are completely external to the valve. The molded sleeve is referred to as the valve body. Pinch valve bodies are manufactured of natural and synthetic rubbers and plastics which have good abrasion resistance properties. These properties permit little damage to the valve sleeve, thereby providing virtually unimpeded flow. Sleeves are available with either extended hubs and clamps designed to slip over a pipe end, or with a flanged end having standard dimensions.

Pinch Valve Bodies Design: Pinch valves have molded bodies reinforced with fabric. Pinch valves generally have a maximum operating temperature of 2500 F. At 2500 F, maximum operating pressure varies generally from 100 psig for a 1-inch diameter valve and decreases to 15 psig for a 12-inch diameter valve. Special pinch valves are available for temperature ranges of -1000 F to 5500 F and operating pressures of 300 psig. Most pinch valves are supplied with the sleeve (valve body) exposed. Another style fully encloses the sleeve within a metallic body. This type controls flow either with the


conventional wheel and screw pinching device, hydraulically, or pneumatically with the pressure of the liquid or gas within the metal case forcing the sleeve walls together to shut off flow. Most exposed sleeve valves have limited vacuum application because of the tendency of the sleeves to collapse when vacuum is applied. Some of the encased valves can be used on vacuum service by applying a vacuum within the metal casing and thus preventing the collapse of the sleeve.

Figure 48: Pinch Valve


============================================= (1-2-5-7) Butterfly Valves: A butterfly valve, illustrated in Figure 49, is a rotary motion valve that is used to stop, regulate, and start fluid flow.

Figure49: Typical Butterfly Valve

Butterfly valves are easily and quickly operated because a 90o rotation of the handle moves the disk from a fully closed to fully opened position. Larger butterfly valves are actuated by handwheels connected to the stem through gears that provide mechanical advantage at the expense of speed.


Butterfly valves possess many advantages over gate, globe, plug, and ball valves, especially for large valve applications Fig 50 . Savings in weight, space, and cost are the most obvious advantages. The maintenance costs are usually low because there are a minimal number of moving parts and there are no pockets to trap fluids.

Figure 50 : A large lined double-flange butterfly valve


Butterfly valves are especially well-suited for the handling of large flows of liquids or gases at relatively low pressures and for the handling of slurries or liquids with large amounts of Suspended solids, so its parts are manufactured in a wide range of materials , Table 15 indicates some popular options

Table 15 : Butterfly valve materials of construction

Standard butterfly valves are mass-produced in a very wide range of sizes and pressure ratings. Table 16 indicates the more popular choices.

Table 16 : Butterfly valves sizes and pressure ratings

(1) Fire-safe

Butterfly valves are built on the principle of a pipe damper. The flow control element is a disk of approximately the same diameter as the inside diameter of the adjoining pipe, which rotates on either a vertical or horizontal axis.


When the disk lies parallel to the piping run, the valve is fully opened. When the disk approaches the perpendicular position, the valve is shut. Intermediate positions, for throttling purposes, can be secured in place by handle-locking devices.

(1-2-5-7-1) Butterfly Valve Design: 1- Butterfly Valve Seat Design: Stoppage of flow is accomplished by the valve disk sealing against a seat that is on the inside diameter periphery of the valve body. Many butterfly valves have an elastomeric seat against which the disk seals. Other butterfly valves have a seal ring arrangement that uses a clamp-ring and backing-ring on a serrated edged rubber ring. This design prevents extrusion of the O-rings. In early designs, a metal disk was used to seal against a metal seat. This arrangement did not provide a leak-tight closure, but did provide sufficient closure in some applications (i.e., water distribution lines).

2- Butterfly Valve Body Design: Butterfly valve body construction varies. The most economical is the wafer type that fits between two pipeline flanges. Another type, the lug wafer design, is held in place between two pipe flanges by bolts that join the two flanges and pass through holes in the valve's outer casing. Butterfly valves are available with conventional flanged ends for bolting to flanges, and in a threaded end construction.

3- Butterfly Valve Disk and Stem Assemblies: The stem and disk for a butterfly valve are separate pieces. The disk is bored to receive the stem. Two methods are used to secure the disk to the stem so that the disk rotates as the stem is turned. In the first method, the disk is bored through and secured to the stem with bolts or pins. The alternate


method involves boring the disk as before, then shaping the upper stem bore to fit a squared or hex-shaped stem. This method allows the disk to "float" and seek its center in the seat. Uniform sealing is accomplished and external stem fasteners are eliminated. This method of assembly is advantageous in the case of covered disks and in corrosive applications. In order for the disk to be held in the proper position, the stem must extend beyond the bottom of the disk and fit into a bushing in the bottom of the valve body. One or two similar bushings are along the upper portion of the stem as well. These bushings must be either resistant to the media being handled or sealed so that the corrosive media cannot come into contact with them. Stem seals are accomplished either with packing in a conventional stuffing box or by means of O-ring seals. Some valve manufacturers, particularly those specializing in the handling of corrosive materials, place a stem seal on the inside of the valve so that no material being handled by the valve can come into contact with the valve stem. If a stuffing box or external O-ring is employed, the fluid passing through the valve will come into contact with the valve stem.

---------------------------------------------------------- (1-2-5-8) Needle Valves: A needle valve, as shown in Figure 51, is used to make relatively fine adjustments in the amount of fluid flow. The distinguishing characteristic of a needle valve is the long, tapered, and needlelike point on the end of the valve stem. This "needle" acts as a disk. The longer part of the needle is smaller than the orifice in the valve seat and passes through the orifice before the needle seats. This arrangement permits a very gradual increase or decrease in the size of the opening

to achieve flow regulation . Also used in instrument impulse (110) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

lines to attenuate pressure pulsations to limit gauge reading fluctuations. Some needle valves are not recommended for isolation purposes, so product specifications must be checked carefully. Like globe valves there is a preferred direction of flow; fluid enters the bottom of the seat, travels up the taper and exits from the top. It is generally used for applications of very accurate throttling at high pressures and temperatures like instrumentation, and gauging. Valve size is limited at very small diameters. . (1-2-5-8-1) Needle Valve Applications: Fluctuated pump discharge pressure to governors and indicators must be minimized by needle valves to minimize the effects of fluctuations in their performance. Needle valves are also used in some components of automatic combustion control systems where very precise flow regulation is necessary.

Figure 51 :Needle Valve

(1-2-5-8-2) Needle Valve Design: Nneedle valves are manual valves intended for continuous throttling to achieve flow regulation. Valves are fitted in


circuits to allow the flow to be adjusted to suit variable operating conditions. They are also used in instrument impulse lines to attenuate pressure pulsations to limit gauge reading fluctuations. These "meter" valves are of a more strong construction. Some valves have accurate calibration, micrometer style scales, to permit repeatability. The stem of a needle valve is machined to an accurate taper and small valves can have a very sharp point on the end. The seat, a much longer seat than in other valves, is machined to the same taper. On opening, the valve creates a long narrow parallel flow passage. As the stem is withdrawn the flow passage enlarges and reduces the flow losses. Needle valves impose high losses in a circuit and have low Cv values compared to other valve types. The nature of the flow passage excludes solids handling , so, clean fluids are essential for acceptable component lives. In general, straight needle valves are small, up to DN25 is usual. Valve bodies can be forged with integral bonnets to remove a potential leak path and solve the connection problem. Most valves have rising stems. The needle portion may or may not rotate depending upon the detailed design. Some valves do not have a backstop which allows the stem to come out of the bonnet. This is not a good idea with hazardous fluids. Stem sealing can be by adjustable packing or by "O" ring. The stem thread may be under the packing or above it. Typical specifications are for valves up to DN 15 to be suitable for 689 barg, up to DN25 for 414 barg. Valves with closed die-forged bodies or machined from barstock can have severe limitations placed on the port sizes. Port machining is only possible through the connections and the bonnet opening. Inlet and outlet passages must be drilled at an angle through the connection openings, see Figure 51.The small diameters may increase the fluid flow losses.


Additionally, the sharp corners formed during manufacture may induce cavitation in liquid applications. One type of body design for a needle valve is the bar stock body. Bar stock bodies are common, and, in globe disk types, a ball swiveling in the stem provides the necessary rotation for seating without damage. The bar stock body is illustrated in Figure 52. Needle valves are frequently used as metering valves. Metering valves are used for extremely fine flow control. The

Figure52: Bar- Stock Instrument Valve

thin disk or orifice allows for laminer flow characteristics. Therefore, the number of handwheel turns can be directly correlated to the amount of flow. A typical metering valve has a stem with 40 threads per inch. Needle valves generally use one of two styles of stem packing: an O-ring with TFE backing rings or a TFE packing cylinder. Needle valves are often equipped with replaceable seats for ease of maintenance.


Types of Valves Summary: * Gate valves are generally used in systems where low flow resistance for a fully open valve is desired and there is no need to throttle the flow. * Globe valves are used in systems where good throttling characteristics and low seat leakage are desired and a relatively high head loss in an open valve is acceptable. * Ball valves allow quick, quarter turn on-off operation and have poor throttling characteristics. * Plug valves are often used to direct flow between several different ports through use of a single valve. * Diaphragm valves and pinch valves are used in systems where it is desirable for the entire operating mechanism to be completely isolated from the fluid. * Butterfly valves provide significant advantages over other valve designs in weight, space, and cost for large valve applications. * Check valves automatically open to allow flow in one direction and seat to prevent flow in the reverse direction. * A stop check valve is a combination of a lift check valve and a globe valve and incorporates the characteristics of both. * Safety/relief valves are used to provide automatic over pressurization protection for a system. * Pilot-operated valves are designed to open and close by a fluid pressure acting on a surface of two opposed pistons which are being connected to the valve plug stem and are operated by fluid coming from a pilot called solenoid valve. * Solenoid valves are small valves used to direct fluid flow between several ports according to an electric control signal. ****************************************************

(1-2-6) Classification By Operating Method: This classification depends on the type of valve,s actuator:- **********************************************


2- ACTUATORS Introduction: The actuator is a device mounted on the top of the valve and connected to its stem to keep the disk of the valve at the required position to stop or pass or throttle the flow.

(2-1) Classification of the actuators: Valves can be classified according to the method by which the valve is operated as follows in Fig 53 :-

Figure 53 : Actuators Classification Diagram

(2-1-1) Manual – Operated Actuators: In this method the valve is furnished with handwheel , the diameter of this handwheel depends on the valve size and the differential pressure on both sides of its closure element when the valve is closed. The diameter increases when size and differential pressure increase in order to open and close the valve by man power, there different types of this method:-

(2-1-1-1) Handwheels Fixed to Stem: As illustrated in Figure 53, hand wheels fixed to the stem provide only the mechanical advantage of the wheel. When these valves are exposed to high operating temperatures, valve binding makes operation difficult.


Fig 53: Fixed Handwheel Actuator

Figure 54: Hammer Handwheel (2-1-1-2) Hammer Handwheel: As illustrated in Figure 54, the hammer handwheel moves freely through a portion of its turn and then hits against a lug on a secondary wheel. The secondary wheel is attached to the valve stem. With this arrangement, the valve can be pounded shut for tight closure or pounded open if it is stuck shut.


(2-1-1-3) Gears: If additional mechanical advantage is necessary for a manually-operated valve, the valve bonnet is fitted with manually-operated gear heads as illustrated in Figure 55. A special wrench or handwheel attached to the pinion shaft permits one individual to operate the valve when two individuals might be needed without the gear advantage. Because several turns of the pinion are necessary to produce one turn of the valve stem ,the operating time of large valves is exceptionally long. The use of portable air motors connected to the pinion shaft decreases the valve operating time.

Figure 55: Manual Gear Head

(2-1-2) Automatic – Operated Actuators : In case of large size valves and when the valve is mounted in a piping system being operated by a control system, the valve must be furnished with an actuator to operate the valve, there

are different types of actuators . (117) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

Valve actuators are selected based upon a number of factors including torque necessary to operate the valve and the need for automatic actuation. To operate effectively, the actuator must be sufficiently powerful to operate the valve and quick response to a control signal.In the event of signal failure the actuator may be required to return the valve to a predetermined position or to hold its current position. It is therefore important to specify the correct type and size of actuator in order to meet the demands of the process, reliability and economy. Here below we will explain the main actuators theory and their assemblies:-

(2-1-2-1) Pneumatic Actuators: Pneumatic actuators provide for automatic or semiautomatic valve operation. These actuators translate an air signal into valve stem motion by air pressure acting on a diaphragm or piston connected to the stem. Pneumatic actuators are used in throttle valves and for open-close positioning where fast action is required.

1- Diaphragm Actuator: In this actuator pressurized air is acting on the surface of a diaphragm against spring force to close or open the valve. When air pressure closes the valve and spring action opens

the valve, the actuator is termed direct acting as it is illustrated in Figure 56. (When air pressure opens the valve and spring action closes

the valve, the actuator is termed reverse acting as it is

illustrated in Figure 57. Adjusting screw is used to adjust the spring force.The pneumatic diaphragm is probably the most widely used and probably the cheapest. Diaphragm actuators may require a pressure reducing


regulator to ensure the applied air pressure is not too high. Most piston actuators should operate successfully at plant air pressure. A filter/drier would be a wise precaution.

Figure : 56 Figure : 57

2- Piston Actuator: Piston actuators are also called "cylinder actuators". Piston actuators are generally used in applications where the stroke

علم صدقة جاريه لروح من أعدهاللهم اجعل هذا ال (119)

of a diaphragm actuator is too short or the thrust too small. They can operate at higher pressures and in some applications a pressure reducing regulator may not be necessary. They are very useful for linear isolating valves such as gate valves. Short stroke piston actuators are available. Figure 58 shows a single acting piston pneumatic actuator with spring return and a positioner fitted for control valve applications.

Figure 58 : A Single Acting Piston Pneumatic Actuator

Piston actuators can be considered as high pressure pneumatic actuator. Single acting spring return actuators are available for mostly "on/off" isolating valve applications. The double acting versions Figure can be used on control valves when good position holding is required under varying valve load conditions. The principle of operation involves creating modulated reciprocating motion by increasing or decreasing air pressure simultaneously on either side of a piston. The air is supplied at high pressure, 6 to 10 barg, which quickly fills the cylinder volume. Piston actuators therefore have an inherent rapid


response for a given input signal. Actuators with plastic pistons and/or cylinders may be limited to 6 barg air pressure. Figure 59 shows a typical double acting piston actuator with an in-line positioned fitted.

Figure 59 : A double acting piston actuator with in-line positioner

The advantages of a piston actuator are:

It can apply a greater thrust than an equivalent area diaphragm actuator due to higher working pressure.

Operates more rapidly than diaphragm actuators because of the smaller working volumes and the higher operating air pressures.

Greater inherent "stiffness" (can be 10 times stiffer than a diaphragm), enables higher precision positioning.

Greater stiffness promotes better position holding under varying valve thrust conditions.

Greater stiffness enhances vibration damping. (121) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

It may not need a pressure regulator for on/off isolation applications.

3- Vane actuator: The vane actuator is a simple mechanism for quarter turn applications. The vane actuator produces rotary motion directly by applying air pressure to an arm or "vane" attached to the spindle.

Figure 60 : A 90o vane actuator with return spring

لروح من أعدهاللهم اجعل هذا العلم صدقة جاريه (122)

Because the vane is attached directly to the spindle there is no backlash or lost motion. The arm has seals on all edges. A split casing is assembled around the vane and totally encloses it. When air is applied to one side of the vane a torque is produced which affects the spindle directly, without translation or transmission losses. The torque produced is directly proportional to the differential pressure across the vane. Travel stops can be fitted in the casing edges to prevent over travel and overload in both directions. Vane actuators can be single and double acting. Clock type torsion springs can be used for spring return applications by adding a spring housing on top of the actuator casing, see Figure 60. By adding a spring, vane actuators can fail-open or fail-closed in the event of power failure. Most actuators require high quality air, but vane actuators can accept poor quality air. However, depending upon the type of vane seals used, lubricated air can be acceptable and entrained solids up to 40 μ m are possible. Vane actuators can be supplied to operate with hydraulic oil. Gearboxes can be added to extend the operating travel up to 180o . Vane actuators are generally small, producing torques up to 200 Nm with 6 barg air pressure. They are probably better suited for butterfly valves than for ball or plug valves. In the context of producing rotary motion, vane motors for compressed air and compressed liquid are available as drivers. These motors are multi-turn drivers in the same sense as electric motors. Vane motors can be used to actuate both linear and rotary valves by fitting a suitable speed reduction and motion translator. Linear valves, for example, can be actuated by using the vane motor to drive the nut in a similar manner to electro-mechanical actuators. Vane motors can be considered when electricity is unavailable or for hazardous areas.

4- Electro-pneumatic actuator: (123) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

Electro-pneumatic actuation uses both compressed air and electricity to operate the valve whether the valve actuator is a diaphragm or piston or vane. This type of actuation is very simple and is ideal for on/off isolating valve applications. As these valves use solenoid valves they can be operated remotely with ease. Both spring return and double acting actuators can be used. Diaphragm actuators may require a pressure reducing regulator to ensure the applied air pressure is not too high. Most piston actuators should operate successfully at plant air pressure. A filter/drier would be a wise precaution. Electronics, PLCs, and pressure/flow transducers or transmitters enable this type of actuation to become DIY controllers. The output from process transducer is connected to a PLC. The PLC logic decides whether the value is correct, too small or too big. If necessary the PLC sends signals to solenoid valves to open or close and adjust the valve one way or the other. Speed control can be implemented by using solenoid valves in parallel. Any character/sat/on of the valve motion required is performed in the PLC logic algorithm. Complicated set pattern operating routines can be performed by the PLC, without operator intervention, triggered by set points in the operating conditions or timed by the PLC. The PLC can also manage alarm and trip set points, as well as variable routines for ESD overrides, based on operating conditions when the ESD signal is received. As PLCs are inexpensive, complex control mechanisms can be implemented inexpensively.

(2-1-2-2) Electric Motor Actuators (Electro-Mechanical

Actuators): Electric motor is used to permit manual, semi-automatic, and automatic operation of the valve.Motors are used mostly for open-close functions, although they are adaptable to


positioning the valve to any point opening . The motor is usually a, reversible, high speed type connected through a gear train Figure 61 to reduce the motor speed and thereby increase the torque at the stem. Direction of motor rotation determines direction of disk motion. The valve may be operated electrically in two ways: semi-automatic when it is operated from the local pushbutton switch, and automatic as when it is operated by a signal from a control system. The electrical actuation may be isolated by a clutch to permit manual operation by a handwheel, which can be engaged to the gear train, provides for manual operating of the valve.

Fig 61: Electric Motor Actuator

A handwheel is often required to operate the valve manually, when starting up a process or in case of emergency; or sometimes a handwheel is used to limit the valve travel. Limit switches are normally provided to stop the motor automatically at full open and full closed valve positions. Limit switches are operated either physically by position of the valve or torsionally by torque of the motor.


This actuator can produce all the required motions for valve actuation:

Linear

Part-turn, 90o or 180o

Full turn, 360o

Multi-turn Electro-mechanical actuators can easily be adapted to suit most types of valve. Electrical safety must be observed when operating in hazardous areas and the ambient temperature in process area must be considered for cooling requirements. Beware of high black bulb temperatures.

Figure 62: Typical electric actuator design

Each actuator consists of a number of components, see Figure 62. Among these are:

An electric motor, low inertia, high torque; dc or single phase, capacitor-run for small actuators, three phase for larger sizes.

Gearing to reduce speed and increase torque. (126) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

Valve attachment according to ISO 5210.

A change-over mechanism to allow local manual operation and to prevent both methods driving simultaneously

Position transmitter to show the valve position locally.

A torque limiter to prevent motor or valve damage and to prevent over travel, see Figure 63.

Figure 63 :Electric torque limiter

Many accessories can be fitted to enhance valve operation, some important ones include:

A switch to select local or remote control when local pushbuttons are fitted.

An intermediate limit switch to allow valve travel to a predetermined position.

An electronic position transmitter, to allow remote indication or control of valve position, see Figure 64.


Figure 64: A 4-20 mA current position transmitter

Figure 65 shows a typical block diagram for an electro- mechanical actuator indicating the various functions available.

Figure 65: A typical electro-mechanical actuator block diagram

Motor starting torque may be slightly less than the stall torque when running; 75 to 80% is normal. Specifying the


number of starts per hour is critical to long term reliability. For isolating valve applications, the standard 60 starts per hour may be more than acceptable. Control modulating applications should specify much higher starting frequencies; up to 1 200 per hour is not uncommon. Actuator cycle times are related to actuator size. For 90o travel a small actuator, 14 Nm, may be adjustable from 5 to 20 seconds. A large actuator, 1080 Nm, may take 1 to 4 minutes. Electro-mechanical actuators for wedge gate valves should be fitted with a "hammer-blow" effect to ensure the valve always opens. Weatherproofing or tropicalisation should be considered for actuators outdoors. Anti-condensation heaters may be necessary for some climates. Flameproof or explosionproof enclosures are available for hazardous locations. For on/off isolating valve applications the actuator opens the valve to a limit switch. Valve closure should be monitored by a torque setting backed up by a limit switch to prevent damage. Valve opening can be monitored by torque setting as well as the limit switch setting. An indicator should always be fitted if the state of the valve cannot be obviously judged. Actuators can be fitted with two motors when used for control applications. A large motor can be fitted for rapid isolation duty in the event of control failure; a smaller motor being used for control modulation. Some actuators for isolating applications can have two-speed motors. Normal valve motion is performed at full speed. The initial valve opening and the final travel on closing can be made at 25% speed to avoid surge and water hammer problems. Electro-mechanical actuators can be the most cost-effective for smaller valves. They are obviously very easy to integrate into digital control system protocols or RS 485, and analogue current signals, 4 to 20 mA. They are the most "stiff" of all the


operating mechanisms, offering the highest positional accuracy and holding. Due to the high ratio of gearing used, electro-mechanical actuators are rarely troubled by vibration or "hunting" problems. Immediate motor reversing is not always uncommon. Actuator cycle times are related to actuator size. For 90o travel a small actuator, 14 Nm, may be adjustable from 5 to 20 seconds. A large actuator, 1080 Nm, may take 1 to 4 minutes. Table 17 shows the capabilities of typical electro-mechanical actuators.

Table 17 : Typical electro-mechanical actuator capabilities

(2-1-2-3) Electro-hydraulic actuator: There are two types of hydraulic actuators:-

1- Double Acting Hydraulic Actuator: Figure 66 illustrates the theory of this actuator. It consists of a piston moves in a cylinder by acting of pressurized oil to get a linear motion to operate linear motion valves or change the linear motion by mechanical mechanism Figure 67 into rotary motion to operate the rotary motion valves. The oil is directed to both faces of the piston by a control system through solenoids valves. A pump and oil sump is used to provide the cylinder with the pressurized oil.


Valves (1,4 ) Open , (2,3 ) Closed in Close Position Valves (2,3 ) Open , (1,4 ) Closed in Open Position

Figure 66 : Hydraulic Actuator Theory

Figure 67: Changing linear motion into rotary motion

2- Single Acting Hydraulic Actuator: This type is illustrated in Figure 68. It is called single acting because one face only of the piston is affected by oil pressure


to give the required motion but the reverse motion is provided by the effect of a spring force. In the Figure, the pressure is directed and then applied to the one face of two opposed pistons against back springs force to impart linear motion which is converted into a rotary motion to the rotary valve stem. The hydraulic oil pressure used to power the system is provided by a small, constantly running, integral eccentric operated plunger pump, driven by an electric motor.

Figure 68 : A hydraulic opposed piston quarter turn actuator

Self-contained electro-hydraulic linear actuators can produce thrusts of over 330 kN; rotary actuators have torques of over 52 000 Nm. Electro-hydraulic actuation can be accomplished in a similar manner to electro - pneumatic actuation by using solenoid valves with standard piston actuators. Both types of electro-hydraulic actuation offer very accurate positioning with "stiff" systems. Hydraulic actuation, with pressures up to 130 barg, have been used to obtain faster valve reactions. Speed increases from 4:1 to 15:1 have been claimed. Hig speed valve operation can create serious problems of surge and water hammer and these effects must be fully


investigated before making binding commitments. Thrusts of over 100 kN can be provided by these actuator units. The integral type actuator/power pack is very useful in remote locations where compressed air is not available.

(2-2) Actuator selection: When selecting an actuator, many factors must be considered: *Compatibility with the valve design to be used. *Power supply for actuator: Pneumatic, Hydraulic, Electric, and Combined system. *Single or double acting. *Control signal for actuator: Pneumatic analogue, Electric analogue, Electric digital, and Analogue / Digital combination. *Force or torque required. *Speed of operation: Slow, Fast, and variable. *Power required to achieve force/torque and speed *Stiffness of actuator. *Fail-safe operation of actuator. Stay-put, Close, and Open. *Accessories and options required: Handwheel, Local powered operation, Positioners, Boosters, Remote indication, ESD override facilities, and Damper. *Ambient operating conditions: Electrically hazardous, Air-borne contamination/corrosion, Water hazards, Temperature extremes, including sunlight, Humidity, Biological attack, Vibration, External and valve- . Generated, Seismic considerations, Serviceability by local, . Staff and reliability . *Initial purchase and installation costs. *Operating and maintenance costs.


A thorough knowledge and understanding of the process to be controlled and its requirements is essential if the correct choice of actuator is to be made. It is not possible to give general advice on the selection of actuators. In the past the pneumatic diaphragm actuator has been the most popular for process applications but electric actuators have been used extensively in small "safe" applications. The advent of cheap electronic controls and digital communications means that "electric" actuators are gradually taking over. NOTES : *Actuator Size: The size of actuator required for a particular valve can be determined by the supplier. Remember that no control valve can control better than its actuator permits. *Booster: A pneumatic amplifier used to convert a pneumatic controller output signal to a higher pressure. The normal controller maximum output of 1.03 barg can be increased to 2.4 barg for higher pressure diaphragm actuators or 10 barg and higher for piston actuators. An air supply about 0.5 bar higher than the maximum actuator pressure is necessary. * Positioner: The positioned Fig 69 supplies air to the diaphragm or piston actuator to adjust the valve in response to control signals. The positioned is coupled to the valve/actuator stem and monitors the valve position to ensure the valve does adjust in response to the control requirement. The feedback of valve stem position allows very precise valve control.


Figure 69 : Schematic arrangement of a bellows positioner fitted to a diaphragm actuator

*Damper: A hydraulic device which can be fitted to power-actuated valves to eliminate spindle/stem vibration and/or control actuation speed. *ESD: Emergency Shut Down is an independent control system within a process plant dedicated to stopping production safely. The ESD uses independent process measurements to detect faults which would cause serious problems. *If response time is critical for process stability then electric power should be considered, but when external electric power is not available the actuator can be driven by the process fluid, in this case the valve of this actuator is called a "regulator",


Any actuator receives electric power or fluid power according to control signal to apply a linear force or a rotary torque to the valve element. The actuator must be attached securely and rigidly to the valve body. A compact assembly is preferable, to reduce space requirements, the chances of accidental damage and the structural vibration problems. ===================================================

3- CONTROL SYSTEM Valves are very important components in any piping system, so their function must be controlled according to the software of the process, some pipe lines have valves in hard terrain, they must be remote-operated, therefore a control system must be designed to control the function of these valves

(3-1) Control Signal: It is a signal from the controller to the final element (Valve)to modulate its position into a new position at which the measured process variable will change near close to the controller set point. If the controller is mechanical, the control signal will be mechanical and pneumatic if the controller is pneumatic, and so on.

(3-1-1) Pneumatic Signal: The pneumatic control valve unit shown in Figure 59 is a completely fluid based system. A pneumatic control signal is piped from the process controller which compares a process fluid signal with the set point. The resulting control signal varies in pressure depending upon the discrepancy between the process variable and the set point. The positioner moves


the valve element in proportion to the pneumatic signal. The controller can be mounted close to the valve, remotely or in the control room. Typical pneumatic control signals are from 0.2 to 1.0 barg.

(3-1-2) Analogue signal: Transmitters and transducers are available to measure the value of the process variable and can produce an equivalent analogue electrical signal in mV or mA, this signal can be translated into the variable value or transmitted to a great distance electrical controller by which the control valve can be controlled by a simple electric analogue signal. One of the most popular electric signals is from4 to 20 mA at 24 V dc where 4mA represents the minimum value and 20mA represents the maximum value of the variable. Using an analogue current signal, rather than an analogue voltage signal, removes problems due to wiring resistance and voltage drop. Other analogue electric signals used are: * 0 to 20 mAdc * 1 to 5 mA dc * 10 to 50 mAdc * 1 to 5 V dc * 1 to 10 V dc Indicating displays can be driven by the analogue signal to allow operator information to be shown at convenient locations. Repeaters, small booster amplifiers, can be used with analogue signals to allow signals to travel very great distances. Typical analogue electric signals are from 0 to 10V or 4 to 20 mA. But of course, only one signal is carried by each pair of wire cores. Sending a great amount of different data requires numerous cores. Digital communications can alleviate this problem.


(3-1-3) Digital Signal: A signal, usually electrical but carries digital information in a series of pulses. A sequence of on-off pulses transmits a binary number.

Figure 70: Simple circuit of digital control

Up to 32 devices can be connected anywhere over a distance up to 4km when using the specified cable type and RS 485 protocol. This type of network is called "multi-drop". If longer distances and more devices are necessary RS 485 can be extended by using line repeaters. The RS 485 protocol can cope with a maximum of 255 devices and transmission speed can be between 100 kbps and 10 Mbps depending upon the cable type and length and the chipset used. Cable lengths shorter than 60 m support the fastest speeds. Cables of the maximum length, 1.2 km, run at the lowest speed. Devices measuring or supplying analogue signals must convert to or from digital signals Fig 70 . The analogue signal is sampled at a fixed intervals and converted to a digital value. The sampling and conversion takes time. Some devices sample


at relatively slow speeds, 1 sample/s to 10 sample/s. This low sampling speed rate may be a problem with some process operations and higher speed devices may be needed. Some protocols are slow, 5 kbps, 31.25 kbps is a popular speed and others are very fast, 12 Mbps. Some protocols have very limited sensor numbers and are best suited to small control networks, such as sensors and control valves in a pre assembled equipment package. Other protocols are capable of connecting many devices. Digital control can be considered at three basic levels of communications: * Device * Distributed control * Supervisory The device level covers relatively short distance connections between sensors/actuators and a local controller or PLC. The distributed control level involves the local controllers/PLCs communicating with a remote PLC or computer. The supervisory level includes the communications between all the remote PLCs or computers to enable the operation of thecomplete system to be viewed and analyzed.

(3-2) Electro control in Actuators Operation: Electronics, PLCs, and pressure/flow transducers/transmitters enable the actuation to become DIY controllers. The output from a transducer is connected to a PLC. The PLC logic decides whether the value is correct, too small or too big. If necessary the PLC sends signals to solenoid valves to open or close control elements to adjust the valve one way or the other.


Table 18 : Process control valve availability and capabilities

Complicated set pattern operating routines can be performed by the PLC, without operator intervention, triggered by set points in the operating conditions or timed by the PLC. The PLC can also manage alarm and trip set points, as well as variable routines for ESD overrides, based on operating conditions when the ESD signal is received. As PLCs are inexpensive, so the complex control mechanisms function can be implemented inexpensively. Linear and rotary control valve types are manufactured in various sizes and ratings. Table 18 indicates the range of linear reciprocating valves, rotary ball valves, and rotary butterfly valves available and the suitability for various operating conditions such as operating temperature, corrosive fluids and flow rates . ====================================================


4- Valve Tests

ن. أق يقللدد للال للجر ءجللراتاا ء للار اصلل . و و للى عللل الصللكللل صللالاد أنللد أق ل للش ق للل ال لل ن مللن ام -مك ونة م قيداً مبا يل :

:)اجلسم( ء ار الغالف(4-1)

اد وقاعدتلله أنللد مللن ء ارهللا ق للل الللدهاق إي للى تعريولله ءك للغن هيدرو لل اتيك نللدوق أر غللالف الصللال -تسلر مل للوت ضلل لغن ا للار ع للدما يكلوق مللرا الصللالاد مغلقلاق ملل. إلل ك السلدا ه ج يللاً و للل ع للد

وء ار الغالف و وأ حيدث تسر من السدا ة ع دما تكوق السدا ة مغلقة أث ات ء ار السدا ة مللرة مللن قيالللة 5و1أو أ يقللل عللن 3-5, 1-5 للغن ا للار أ للى أق يقللل عللن للل ا للد ا اجلللدو -

وف °100 غن ال ص يف ع د و (4) مدة تعريض الصالاد للوغن أث ات ا ار أ تقل عن تل ا د ة ا اجلدو -

(4-1)Shell Test: Each valve must be tested prior to shipment from the manufacture. The manufacturer should submit to the purchaser written test procedures adhering the following:-

- The valve shell and seat must be tested before painting the

valve, it must be subjected to a hydrostatic pressure without

any visible leakage under the test pressure when both ends

are blanked and the closure element is partially open in shell

test and when the closure element is closed in seat test.

- The test pressure should not be less than that specified in

table 19, 21 or not less than 1.5 times the 100°F pressure

rating.

- The duration of the test shall be not less than that specified

in table 22.


Table19: Schedule of test pressure for standard flanged end and standard

weld end valves

Table 20 : Minimum duration of hydrostatic test

Table 21 : Pressures for optional backseat and air seat tests

Table 22 : Minimum duration of backseat and air seat tests

: API 598إ ص الصالاماا وء ارها وإقاً وامواصفة (4-2)

مقدمة : (4-2-1)

م طل اا 1990عاد 598امواصفة ا حد قد الصالاماا اجلديدة أند من ء ارها ابمص . ق ل ش ها و


ر أق حيد ا ملى ال رات م طل اا ء ار الصالاماا ا اراا والف وص والىت مبوج ها يس طي. ام ج

-: الىت قد ت الل ا اراا اآلتية

وء ار غالف أو جسم الصالاد -أ ء ار القاعدة اخللفية للسدا ة )القرص( و - و ا ار ابلوغن ام خفض مدر ءحكاد غلق الصالاد -ج و اد غلق الصالادا ار ابلوغن امرتف. مدر ءحك - و ا ار ابل ظر للالص وابا -ه

و23من الصالاماا مو ة ا اجلدو وتوجد م طل اا لإل ار لكل نوع

(4-2) Valve Inspection and Testing (API 598) : (4-2-1)

General :

The new valve must be tested in the manufacture before shipment. API standard 598 (1990) specifies the tests and examinations requirements by which the purchaser can specify in his purchase order the valves test requirements that may include the following tests: -

a- Shell test.

b- Backseat test.

c- Low-pressure closure test. d- High-pressure closure test. e- Visual examination of castings. There are test requirements for each type of valves table 23.

Table 23 : Pressure test requirements by valve type

م طل اا ا ار : (4-2-2)

ما . ا ار : (4-2-2-1)

ميكن للال جر أق يس خدد غن امات ار الصالاماا , وقد حي ور امات امس خدد ألر ء ار عل زي قانل للذوابق ا امات أو مان. للصدأو وابل س ة للصالاماا امص وعة من الصلى الذر أ يصدأ ) انلس(

و وميكن ا خداد وا ل لإل ار ج ت/ مليوق 100أو امات الذر أ ت يد كلوريداته عن تس خدد مات ال ر . ا ار قد يكوق هوات , غاز امل,وكريو ني اراا الوغن أ ت يد ل وج ها عن ل وجة امات و وما

لإلرتكاز نوغن م خفض ام خفض اخلاصة مبدر ءحكاد غلق الصالاد وابل س ة اراا الغلق والقاعدة اخللفيةو ن. أق يقدد مريقة ك ف ال سر ايكوق ا ار ابهلوات أو الغاز اخلامل وعل الص

(4-2-2) Test Requirements:

(4-2-2-1)Test Fluid:

The purchaser may utilize pressurized water to test the valves, water used for any test may contain a water-soluble oil or a rust inhibitor. For austenitic stainless steel valves, potable water or water whose chloride content does not exceed 100 part/million shall be used. Noncorrosive liquid whose viscosity is not higher than that of water can be used. The test fluid may be air, inert gas, and kerosene for low pressure closure and low pressure backseat tests, when air or inert gas is selected, the manufacturer shall provide the method of leak detection.

رجة حرارة ا ار : (4-2-2-2)

د( و امللا ابل سلل ة لل خداماا الصللالاماا لللدرجاا °52ف )°125 للى أآل ت يللد رجللة حللرارة ا للار عللن حرارة م خفوة إإق رجة حرارة ا ار ميكن أق ت د ا ملى ال رات و

غن ا ار : (4-2-2-3)

ويكوق غن ء ار اجلسم كالا هو مدوق ا اجلدو ي غري غن ا ار وإقاً وما ة تص ي. جسم الصالاد لالنواع امخ لفه من الصالامااو (2)للالوا امخ لفه واجلدو (3)


(4-2-2-2)Test Temperature:

Test fluid temperature shall not exceed 125°F (52°C).

Table 24 : Shell test pressure

Table 25 : Other test pressure

For low temperature applications fluid temperature may be specified in the purchase order.

(4-2-2-3) Test Pressure: Test pressure varies according to the material used to fabricate the valve shell. The shell test pressure shall be as listed in table (24). for different materials, and table (25) for different types of valves.

إجة ا ار : (4-2-2-4)

API 598م قا وامواصفه

ني مده أ تقل عن تل امو ه ابجلدول أند أق ي عرض الصالاد اك غن ء ار ويظل الصالاد عل هذه احلاله26 ,27

Table 26 : Duration of required test pressure

Table 27 : Maximum allowable leakage rates for closure test


(4-2-2-4) Test Duration:

In API 598, the valve must be subject to the test pressure and shall be maintained in this condition for at least minimum time as specified in table 26 and 27.

: ال سر (4-2-3)

ء ا أجللرر ا للار نوا للطة السللا ل إللال للى تهللور نلللل أو ت قللين للسللا ل عللل السللطك اخلللارج لل سللم -امعرض للوغن من الصالاد أو من ال لدا ة الصلالاد أو للف حلقلاا ا حكلاد نقاعلدة ءرتكلاز الصلالاد

األجل ات وأ يقصلد نلذل . اخلرير حو العالو وأيولاً غلري مسلالوح تر ت لوية ألجل ات الصلالادأو ارج مان و ا حكادالىت ي غري شكلها نقصد الطرية أو اللي ة

(4-2-3) Leaking:

- If the test is performed by a liquid, there shall be no wetting

or drops of the liquid at the external side surface of the

pressurized surfaces or through the disc, behind the seat

rings or past the shaft seal. Also no structural damage are

permitted (plastic deformation of resilient seats is not

considered).

لى ا حسلااب ابر تسلر و و لى أأ ي يلد ال سلر وء ا أجرر ا ار نوا طة اهلوات أو الغاز إلال و (5)ع د قواعد ا رتكاز عالا هو مدوق ا اجلدو

- If the test liquid is air or gas, no revealed leakage shall be

detected. Leakage from seats shall not exceed that in

table27.

: ءجراتاا ء ار الوغن (4-2-4) وصف عاد : (4-2-4-1)

واللدهاتا الواقيلة م لل ،ع دما يسل خدد لا ل لإل لار إالنلد أق يكلوق الصلالاد اليلاً ملن اهللوات أث لات ا لارال وايا والىت قد تولل ءك اف العيو من لال األ لطك أ ىلرر ألر لطك ق لل ا لار وأيولاً أر ملا ة

ار ن. أند أق يس خدد مريقة ا ار ءحكاد الغلق إإق الصميكن أق تسد مساد أر خب خةو وع د ءجرات ء قاعدة ءرتكاز السدا ة ءك احلي اموجو نني القاعدة وق ة الصالاد لل أكد من عدد وجو تسر يهر ا اخلرير

تدر ياً ويوغطه ووميأله ءك هذا احلي

(4-2-4) Pressure Test procedures :

(4-2-4-1) General :

When a liquid is used as test fluid, the valve shall be essentially

free from air during the test, protective coating such as paint

which may mask surface defects shall not be applied to any

surface before the test and also any substance that may seal

off porosity. When performing the closure testing, the

manufacturer shall use a method of te-sting seat leakage into

the cavity between the seats and the bonnet to insure that no

seat leak-age can escape and fill this space gradually then

building it up with pressure.

: (اجلسم الغالف) ء ار (4-2-4-2)

يض الصلالاد ملن اللدا ل ءك الوللغن نعلد غللق أمراإله مل. إل ك السلدا ة ج يلاً وءحكللاد ر ل لش جسلم الصلالاد ن علال قرين عل ح و اجلل د مبا يكفل ا اإظة عل غن ا ار , وهبلذا ا لار إلإق غرإلة احل لو يكلوق قلد

أث ات ءجرات ا ارو امطاميه وأند من عدد تهور أر رير حبلقاا ا حكاد ء ارها أيواً

(2-4-2) Shell Test :

Shell test shall be performed by applying the pressure inside the assembled valve with the valve ends closed and the closure element is partially open (to pass the test fluid into the bonnet space), and the packing gland is tight enough to maintain the test pressure, by this test the stuffing box is also tested, shaft seals such as O-rings shall not leak during the shell test.

Backseat : (المسند الخلفى للسداده) A seal found on some valves to isolate the packing box from the valve internal pressure. In rising stem valves the stem can be physically prevented from lifting out by fitting a collar


above the disk which engages an upper back seat and contacts it when the valve is wide open. The seating can be a good metal-to-metal contact or can incorporate a resilient seal. Fluid is prevented from escaping up the stem by the surface contact. Valves in which the internal pressure generates an axial thrust in the stem or spindle can have a pressure loaded backseat bush. The use of a backseat bush allows the packing box to be maintained while the valve is pressurized.

BackSeat

سدا ة : لل اخللف س دام ء ار ءحكاد (4-2-4-3)

للطاقيه الصالاد عل قاعدة ءرتكاز لفية مرك ه عل اق رر هذا ا ار للصالاماا الىت تس د إيها دا ةع دما يصل الساق ءك هناية م وار الف ك إ ط ق السدا ه عل القاعده مانعةالسا ل من ال خلل ءك غرإة احل و

الصللالاد حللىت للر ن سلللين الوللغن ا للل الصللالاد نعللد ىاليلل. أجلل اته ونعللد غلللق مرإيللة ملل. إلل ك ويلل م ا للارع لد من ال اجلل د إلإق لل يعلن أق ا حكلاد سا لح و اجلل د إإ ا حدث تسر لل طوهتوية راب ا م واره

ونني السدا ة ومس دها عيف طك ال المس ح من أعدهاللهم اجعل هذا العلم صدقة جاريه لرو (150)

(4-2-4-3) Disk Backseat Test:

This test is performed for the valves that have backseat on the stem seating on the lower surface of the bonnet at the end of opening stroke, by applying pressure inside the assembled valve when the valve ends are closed, the closure element is fully open and the packing gland is loose, if the fluid leaks from the gland that means seats are not too tight with the closure element to prevent leak through the contact surface.

م خفض: ء ار جو ة الغلق هبوات و غن (4-2-4-4)

ولغن مل خفض علل أحلد نملن كلال مرإيله يسللن هلوات مولغوط وال علرض لولغن ابل س ة للصالاد امصالم للغلق الطللرإني عللل أق تكللوق السللدا ة ا و لل. الغلللق واجلانللى اآل للر مف للوح ءك اجلللو لك للف ال سللر نلله مللن للال

إلإق الولغن ألماقم لل صلالاماا إقلنالسدا ة امغلقةو وابل س ة للصالاماا الىت ت علرض للولغن ملن ملرف واحلد يسلن تحيلة الطلرف امعلرض للولغن إقلن وابل سل ة لصلالاماا علدد الرجلوع إلإق الولغن يسللن ملن جهلة لروج

ا الطلرف امف لوح ع لد تهلور أو القرص من اجلانى امف وح وف يك لف السا ل إقن وأر تسر عش القواعد اللىت تكلوق مغطلاة ءملا ابملات أو مب للو لقواعد أو احللقلاا احلانكلة السدا ة أو امكوتا الغلق ي. أتت حو ققاإ

. الصانوق

(4-2-4-4) Low-Pressure Closure Air Test :

For a valve designed to close against pressure from both directions, the air pressure is applied to one side, the closure element is closed, and the other side is open to atmosphere to detect for leakage from it through the closed element. For valves closed against pressure from one side only, the test pressure shall be applied on the pressure side only. For check valves, the pressure shall be applied on the downstream side on-ly. Any leakage at the seat or through the disc on the open side at the valve shall be detected when bubbles are observed coming from the closure (disc, seat, seat ring) which is either covered with water or soap solution.


: سا ل و غن عاكنء ار جو ة الغلق (4-2-4-5)هللو نفللس ا للار السللانق ابهلللوات إيالللا عللدا أق ا للار ابلسللا ل للوف يظهللر ال سللر إيلله عللل

ء ا كلاق (5)رقلم شكل ت قين وليس إقاقي. عل أأ ي عدر معد ال قين ما هو ملدوق ا اجللدو و الصالاد ليالاً

(4-2-4-5) ) High-Pressure Closure Liquid Test:

it is the same as that for low-pressure closure air test except that in case of a liquid test, leakage shall be detected when drops, not bubbles are observed at a rate does not exceed that is listed in table (5).

: الف ص من جانى ام جر( 4-2-5)

ا د ة ا اراا مدة مخس أايد عالل جرات حوور م دو ع هطر ام جر ن اريخ أند للصان. أق لف ص الصالاد ننوا طة ام جر وأر ء اراا أو إ وص أ رر ء اإية ويقود م دو الف ص للال جر

ارية يا الوغن ء اراا وم اهدة ال رات, ملى ل وصيف الدا لية أج اته مطانقة ل أكد منل والف وصاا وال ها ة عل أر إ وص تكاليلية ومراجعة الا مراق ة جو ة ا ن اج

(4-2-5) Inspection by the purchaser:

The valve manufacturer shall notify the purchaser the date of 5 working days of witnessing the tests specified by the purchaser and any specified supplementary inspections or examinations. Purchaser inspector shall: inspect the valve dur-ing assembly to assure compliance with the specifications of the purchase order of the internal parts, witness of the optional pressure tests and examination, witness of any supplementary examinations, and review of quality control records.

: شها ة الصالاد وءعا ة ا ار( 4-2-6)

شها ة ا ل اد : ( 4-2-6-1)

ن. ى أق يقدد شها ة للال لجر لل امله ن صلوص ال وصليف اع دما يكوق م صوصاُ ا ملى ال رات , إإق الص و ا ملى ال رات


: ا ار تكرار( 4-2-6-2)

عللا ة ا للار ع لدما يكللوق م صوصللاً عليهللا ا مللى ال للرات وميكللن م لدو الف للص ا لل غ ات ع هللا ء ا ىلرر ءن. شها ة مك ونلة تق الصلالاد قلد إ صلة وء لاره وىرن له ابل قيلد ابمواصلفة القيا لية معهلد ال لجو اقدد الص و API 598األمريك

اج ءك ءزالة ال وية ع د ءعا ة ا ار وامطلية ابل وية أ ض اام. مالحظة أق الصالام

(4-2-6) Valve Certification and Retesting :

(4-2-6-1) Compliance Certificate :

When specified in the purchase order, the valve manufacturer shall submit to the purchaser a certificate of compliance with the purchase order.

(4-2-6-2) Retesting: This retesting is performed when it is specified in the purchase

order. It may be waived by the purchaser’s inspector upon

written certification by the manufacturer that the valve has

been inspected, tested, and examined for conformance with

API standard 598.

Painted valves need not have paint removed for retesting but

shall be commercially cleaned before retesting.

: ءرشا اا ال رات( 4-2-7)

ا رشللا اا اآلتيللة تسللاعد ام للجر ا القللراراا الواجللى ء ا هللا اب للاإة ءك ال أكيللد عللل توصلليل امعلومللاا الكاإية ءك الصان.و

: قا الة ال ياتا

API 6Dيبيي ائمميب بيئنيئل الميمئق وفويئا ومواميفب مبتيد البميروى ا مري يى المرفق النموذجالمييى يم يي دسييمخدامتئ لمومييي ومحمييوع ىلييى المبلومييئل 1994مييئر 31فييى 21الطببييب

. الممئق المطلوب والمى يجب أ مبطى للمئنع


(4-2-7) Purchasing Guidelines:

The following guidelines assist the purchaser in decisions he must make, as well as assuring that adequate information is communicated to the manufacturer. Date sheet:


The above form shows a valve data sheet according to API specification 6D (march 1994) contains information that can be used to specify the required valve and that should be given to the manufacturer.

: ار ابموق.ا (4-2-8)

% ع للدما يكللوق الصللالاد مف وحللاً 50 لى أأ ي يللد للغن ا للار ابموقلل. علن أقصلل للغن ت للغيل تك للر ملن لوغن مسلطاً من جانى واحد من الصالاد و % ء ا كاق ا10ج ياً أو مبقدار

(4-2-8) Field Testing:

Valve field test pressure should not exceed the maximum

operating pressure of the valve by mo-re than 50% when the

valve is partially open or by 10% if the pressure is applied to

one side of a closed valve.

: ش ر فالكا اا وال ( 4-2-9)

العازللة نلني شر فلتصلاليم الصلالاد لى أق يراجل. ء ا كلاق مطللوابً أق ميلر ابلصلالاد كا ل اا ت ظيلف اخلطلوط أو ال ام اا ام عاق ةو

(4-2-9) Scrapers and Spheres:

The design and construction of the valve should be examined if

the valve is required to pass scra-pers or spheres.

: ء ار احلريق( 4-2-10)أو امواصفة API 6FAامخ شة لإل خداد ا احلرا ق تصالم حبيث ي واإر إيها م طل اا امواصفة ااالصالام

API 607 و

(4-2-10) Fire Test:

Fire tested valves are designed to be specified in API spec. 6FA or API standard 607.


م طل اا ء اإية لإل اراا: ( 4-2-11)

هذه ام طل اا ء يارية وإقاً وءجراتاا مك ونة من ام جر أو من مي له وت ال ل ا رإ. مق و لوغن ا ار ن ي و ع ه أو ءمالة مدة ا ار عالا هو حمد ا جداو ال وصيف امو ة , نوا طة ام جر أو نوا طة م

والع د امطلو لف ك الصالاد يقااب نوا طة الصان. ع د غن إرق عل جانىب السدا ة و رجة حرارة حيد ها دة ا رتكازام جر و رر ء ار الع د الياً ار الوغن اهليدرو اتيك و انقاً ار ءحكاد قاع

(4-2-11) Supplemental Requirements of the Test:

These requirements are optional in accordance with written procedures by the purchaser or this representative such as higher reasonable test pressure or longer duration than specified in attached tables, and the torque required to open the valve shall be measured by the manufacturer at a differential pressure and temperature specified by the purchaser, torque test shall be performed subsequent to the hydrostatic shell test and prior to any seat test.

5- Installation

5-1 Introduction: Valves can be a source of constant trouble on site. Purchasing valves to a price rather than to a specification may be another problem. The costs of valve failures must be considered during the process design and valve selection phases and arrangements made to cope with costly problems. Whole-life cost is likely to be many times greater than the initial purchase cost. "Read the instruction manual first!" Information from similar installations is very useful but must be used with care. Many valve manufacturers hold training courses at their


works in which all requirements for training are available to

explaining all aspects of operation and maintenance and also training staff and their equipments travel to long distances, can be extremely costly .This is a very good investment in the long term. Manufacturers spend considerable effort and money preparing and printing manuals to promote successful operation of their valves. Operating and instruction manuals should be stored efficiently at user site to allow maintenance staff on site to rapid reference in case of breakdowns. During normal working a log of operating conditions should be routinely updated. Background operational history will prove invaluable when investigating problems and failures.

5-2 Pre-installation inspection: Before erecting pipe sections, site staff must ensure all relevant equipment is available. Terminations at the beginning and end of the pipe run must be ready to accept the pipe. All intermediate valves and fittings should be present and moved to their final locations. Valves which are "adjustable" such as safety relief valves, regulators and control valves should be tested, if possible, before installation. Some non-return valves are adjustable but pre-installation testing may not be possible due to the wide range of operating possibilities. Testing during commissioning will probably be the only suitable option. Valve testing should, ideally, be performed as soon as the valve is received at site. There are several good reasons for this recommendation: The test will establish whether the valve conforms to its specification in all respects. It is therefore necessary to have


the manufacturer's specification available and the process

data sheet for the valve, and to confirm every design feature and every function of the valve. The tests should also check features not expressly stated in the manufacturer's data sheet, such as seat or gland leakage, friction or hysteresis of the actuator. A pressure test at the stated test pressure(s) may be necessary if the factory test certificate has expired. Legal requirements for some systems dictate retesting routinely at specified time intervals. The site test record is the basic datum for all subsequent maintenance operations. If the valve is used in corrosive service, a record of body thickness or trim clearances will establish the rate of corrosion of affected parts and their replacement. A check of regular and special spare parts will ensure that these can be ordered in time. It should be evident that testing should be done as early as possible, so that if a defective valve has to be returned to the manufacturer, it will not cause serious delay to a construction program or a maintenance schedule. After workshop testing, valves should have the inlet and outlet blanked off with plywood and adhesive tape to avoid contamination and entry of dirt or stones, before being returned to storage. Pipework can be installed initially with safety relief valves, regulators and control valves replaced by spool pieces. This allows the pipe system to be cleaned without damaging valves.

5-3 Test equipment: It is possible to obtain proprietary test stands to perform the first three tests listed above; but the equipment is quite simple to construct and many larger sites using "adjustable" valves may prefer to build their own. A simple test stand should accommodate valve bodies from


DN25 to about DN100. Some larger sites may need to test

valves up to DN 150 but the majority of valves will be DN 100 and smaller. Mobile test facilities and staff may be available for large valves. Before building a test stand it is advisable to check the local support companies for suitable test facilities. The valve should be securely attached to the test stand by its inlet connection, which also acts as a feed for the water supply for pressure and leak testing. The outlet connection of the valve should be blanked off and fitted with a small valve for venting the air from the body. Test stands in which the valve under test is sandwiched between two flanges tightened by a screw jack are not recommended. A mobile hoist of the type used in garages is very convenient for removing actuators and bonnets, etc. The test stand also supports the valve during seat removal, grinding-in and some of the other maintenance operations on the open body described later. The test stand should be fitted with two air supplies that are adjustable between zero and the highest actuator pressure encountered on site. One of these supplies is used as the main air supply to valve positioners, piston actuators etc., and should be fitted with a simple regulator and gauge to allow it to be set to the correct value. The other supply should be controlled by a precision regulator and the air pressure indicated on an accurate gauge. This gauge, because it is a calibration substandard, should be included in the regular calibration program on site of all test equipment. To perform pressure and leak testing at the specified pressures for each valve, a supply of high pressure water is required. Such a supply is most conveniently generated by a direct acting air-operated reciprocating pump. This type of pump is driven by a regulated supply of compressed air and is capable of furnishing exact test pressures from a few bar to thousands of bar. This pump, with suitable connectors and hoses, will beable to pressure test all valves on site.


Safety relief valves can have the set pressure checked with the

high pressure water supply. The flowing characteristics of a valve, overpressure and blowdown, can only be validated with an adequate supply of appropriate fluid. In the same way in which these tests are carried out before the "adjustable" valve is installed for the first time, they should be performed on each occasion the valve has been removed from the plant for service.

5-4 Installation criteria: 5-4-1 Pipework: Valves must be installed correctly if a long, economic service life is to be achieved. Pipe "fall" must ensure adequate venting and draining. Hazardous liquids should be capable of complete drainage to suitable collection points. The pipework must have adequate flexibility to prevent excessive forces and moments being applied to the valve body; distortion can induce seat leakage and promote galling/wear/seizure of trim. Piping and valves in areas of high fire risk should have the effects of high ambient temperatures fully investigated. Under these circumstances it may be advisable to upgrade flange ratings to provide higher gasket loads or use RTJ metal gaskets or clamped connections with metal seal rings. Safety relief valves, specifically for pressures generated by fire hazards, may be necessary. Safety relief valves that protect against thermal expansion caused by normal ambient temperature changes may be required in pipe sections locked between two isolating valves. Many high integrity systems utilize socket or butt weld valves. The manufacturer's instructions should be reviewed for disassembly requirements prior to welding and adequate protection must be applied for weld splatter. Butt weld valves can be removed from pipework and replaced after the old welds have been dressed. Socket weld valves and fittings are


much more difficult to remove. Threaded pipework can be damaged by Stilsons wrenches, Footprints, pipe pliers and chain wrenches during installation. This type of damage can be serious on galvanized pipework and pipework susceptible to fatigue failure. Care must be taken during assembly to prevent damage which can shorten the working life of new equipment. Great care must be taken with the design of threaded pipework systems. It is easy to design a system which cannot be assembled or a system which requires remote connections to be broken to allow the removal of a specific item. These problems may not become apparent until the system assembly stage. Thread paste should be applied to the pipe and not the valve body threads, otherwise paste may enter the valve trim where it will collect dirt and possibly prevent the valve from closing. For valves with flanged connections, check that the flanges are properly aligned to ensure even gasket contact. Fit the bolts and tighten the nuts in the order shown in Figure 71 This will prevent uneven loading on the gasket and risk of flange breakage.

Figure 71: Flange bolting tightening sequence

5-4-2 Valve mounting: The physical location of valves within the pipework is


important. Valves should not be positioned close to fittings which create severe flow disturbances. Uneven flow patterns can cause unexpectedly high erosion and rapid wear. Regulators and control valves can suffer continuous or intermittent instability due to irregular flow patterns. If a valve must be located close to a bend then a "pulled" large radius pipe bend is preferred to a bend fitting. Valves should not be located at the centre of spans between pipe supports. The increased pipe deflection may lead to vibration problems. The physical location of valves to enable ease of personnel access may be very important, even for automatic valves, since all valves will require inspection at sometime. Some, however, can only be maintained/repaired in situ. Valve internals can be inspected with a boroscope if a small connection is available. Fixed valves with integral seats may require machining or lapping in situ. Access must be considered as an integral part of plant layout, and valves should be located where the complete external condition can be easily seen. Additional instrumentation should be considered when routine inspection visits are not possible. Some standard valves are not suitable for mounting upside down or in vertical pipe runs. The actual mode of mounting may not be apparent until assembly at site. Manufacturer's installation instructions should be consulted for acceptable mounting positions. Adjustments may be possible to accommodate various positions. Regulators and control valves are best installed so that the actuator is vertically above the valve. The actuator should be adequately supported to avoid vibrationproblems. Preservatives on valves should be removed just prior to installation. The manufacturer's instructions will state the appropriate solvents required. Valves for biotechnical and hygienic applications must be cleaned thoroughly with suitably approved solvents.


Piping systems which operate at low or high temperature may be surrounded by substantial layers of insulation and metal protective cladding. The glands of valves should be left exposed for easy, visual inspection and maintenance. The early signals of packing wear, liquid drips and vapor clouds, can be concealed by insulation. Maintenance staff can easily adjust a gland when passing on another job. Stripping insulation for an inspection will only be done as a specific scheduled task. Carbon steel pipework expands approximately 1.2mm per meter per 100o C temperature rise, and stainless steel slightly more, at 1.7mm. The change in pipe length, and consequential forces and moments on connections, must be considered. Manual valves can generally be mounted with the spindle /stem vertically above the valve or extending horizontally. If the valve is to be mounted in any other orientation check the operating instructions. In general, manual valves with packing boxes should not be mounted upside down. Most solenoid valves must be mounted with the armature vertical, directly above the valve. Some valves will allow a small deviation from the vertical, + 15o so it is important to check the operating instructions. Safety relief valves, srvs, must be installed correctly if the safety function is to be achieved successfully. The inlet pipe for a srv should be as short as possible. When protecting a vessel or boiler, direct connection to the vessel flange is preferred. If inlet piping is unavoidable then the pipe should be at least one size larger than the valve inlet.

NOTE: Never fit a valve to a connection which is smaller than the valve inlet. If the pipe length is significant or the viscosity is high check the pressure drop at the maximum flow rate. This should not exceed 3% of the valve set pressure. Inlet pipes for liquid valves must ensure a good supply of


liquid and eliminate the possibility of gas or vapor reducing the valve capacity. Inlet pipes for gas and vapor should "fall" back to the source to avoid the accumulation of condensation and liquid slugs. Hot inlet piping should be insulated up to the srv. Outlet pipework should be free flowing, about 10% friction drop maximum. During pressure drop calculations remember that gas and vapour will expand considerably in the srv outlet pipe. When multiple valves are piped to a common outlet or the outlet pipe is used for other functions, the design must be considered carefully. Do not cost cut on pipe sizes. Outlet pipes must be self-draining. Liquid or condensation must not be allowed to accumulate on top of the plug and cause corrosion. A separate drain pipe on the main outlet pipe may be necessary to ensure drainage. Some srv designs include pockets within the valve body which cannot be drained. Check valve designs carefully if corrosion is likely to be a major problem. For example- Can a drain pipe be fitted to the valve body? Bends in the outlet pipe can transmit forces and moments back to the valve body so adequate pipe supports must be fitted. The back pressure at the valve outlet should remain relatively constant over all operating conditions. Variable or significant back pressures require balanced bellows or pilot-operated valves. The reaction force caused by the valve operation must be absorbed by the pipework. Additional local supports may be necessary. Some srvs are installed with standard isolating valves in the inlet pipework. This practice is prohibited by many pressure vessel and system "Codes" and classification bodies. This type of installation is understandable, but not approved, when the process must continue to operate with defective valves. If


isolating valves are to be fitted in this way then valve locking must be strictly observed. Only very senior operating personnel must have the authority to take the srv off-line. Srvs are normally mounted with the spring vertically above the plug. Low pressure valves may be mounted upside down when specifically instructed by the manufacturer. Mounting in otherm positions is at the manufacturer's discretion. Srvs can be fitted with manual lifting levers to allow lift checking and also to enable solids to be blown off the seat. Good personnel access is necessary to benefit from this facility. Extension chains or rods may be fitted to allow operation from below. Hydraulic or pneumatic cylinders can be fitted to allow remote operation. Some srv designs result in the inlet flange being much thicker than normal and so extra long studs or studbolts may be required. Gas and steam srvs can produce a lot of noise when operating.


Figure 72 :Type I Control valve manifold dimensions for ANSI Class 300LB

Large valves may require large silencers to become socially acceptable. The problem of valve noise must be considered at the design and selection stage. Silencers are likely to be too large to be fitted as an afterthought. Two identical srvs can be fitted with a special double-beat globe valve in the inlet pipework, one working valve and one 100% standby. The standby valve becomes available when the globe valve is changed over. The valve outlets are piped independently. This type of installation allows continuous protection with the facility for standby maintenance and inspection. When the outlet pipe is long a similar type of valve can be fitted to the valve outlets allowing the working valve to utilise the single outlet pipe. The inlet and outlet globe valves can be "ganged" together using a chain drive from one stem to the other.


Bursting discs can be used as standby protection while srvs are being maintained. It is advisable to ensure that a stock of replacement discs is always held. The ISA has recommendations concerning the space which should be allowed for a regulator or control valve in a pipe system.The importance of following these recommendations becomes evident as soon as it is necessary to service the valve or replace components with the valve in situ. The tables in Figures 72 and 73 refer to cast steel valves although they can also apply to cast iron valves. Regulators and control valves are frequently used in systems with compressors and pumps which create flow variations and pressure pulsations. Reciprocating and peristaltic machines may be fitted with pulsation dampers to attenuate the effects on pipework. Most compressors and pumps produce pressure pulsations to a greater or lesser extent and dampers or pulsation filters may be fitted to prevent control instability. During regulator/control valve installation, especially with


Figure 73: Type Vl Control valve manifold dimensions for ANSI Class 300LB

reciprocating machines, check the piping to see ifdampers /filters specified have been fitted or are still in storage. Waiting until commissioning may result in long delays. During system assembly it is sensible to check the pressure ratings of the pipes, fittings, flanges and valves used. The system can only be operated and hydrotested at pressures compatible with the lowest rating. With large, complex process systems the pipework and valves may be assembled some considerable time before the process is commissioned. It is essential therefore that valves are protected, internally and externally, against corrosion and physical damage. The internal conditions, prior to start-up, can be much more corrosive than the normal operating conditions. 5-4-3 Instructions of Valves for Piping System :


شبكة األنابيب:إرشادات عند تركيب الصمامات فى

إرشادات عامه: ى تركيى الصالاماا حبيث تكوق يقاق ت غيلها نني امس ور الرأ وا إق م. األ ذ ا ا ع ار ى ى

ءصطداد الرأاب أو الرك ة ابلساق وأأ تكوق السيقاق األإقية ا مس ور عني امس خدمني و الصالاماا امدارة ها ا و . رأ قا م حىت يسهل تركيى احلوامل هلا وءجرات الصيانة الالزمة ونوا طة موتوراا ك رية ى تركي

ى تركيى الصالاماا ع د ال قطة الىت ميكن الوصو ع دها للصالاد و الصالاماا امرك ة عل ال كاا امرتفعة عن األرض والىت تكوق يقاق ت غيلها أإقية ى أأ ترتف. أ ىن

مج( إوق األرض أو الرصيف أما الصالاماا الىت أ ي كرر ء خدامها 2قدد ) 5و6نقطة لطارة الصالاد عن إيالكن أق ترتف. عن هذا احلد عل أق يس خدد اجل ير ا إ ها أو ءعدا رصيف مرتف. اص هبا و

ع د ء خداد اجل ير ا ت غيل الصالاماا ى ء يار مكاق الصالاد حبيث أ يس ى اجل ير طورة عل العاملني ابل غيل و المة

مم( و 100نوصة ) 4 ى ترك إراغ حو مارة ت غيل الصالاد أيقل عن ى عدد تركيى الصالاد مقلوابً )الطارة أ فل الصالاد( و ى ترك إراغاا حو الصالاد تسالك ل خراج أر قطعة من وا ل الصالاد و

General Instruction:-

Valves should be installed with the stems between the

vertically upward and horizontal to avoiding head and knee

knockers, and valve stems in the horizontal plane at eye level

that may be a safety hazard. Large motor-operated valves

should be installed in the vertical upright position where

possible to facilitate support and maintenance

Valves should be located at accessible points in the piping system.

Valves in overhead piping with their stems in the horizontal position should be located such that the bottom of the handwheel is not more than 6.5 ft (2 m) above the floor or platform. Only infrequently operated valves should be located above this elevation and then the de-signer should


consider the use of a chain operator or a platform for access .

Where chain operators are used, the valves should be located such that the chain does not present a safety hazard to the operating personnel.

A minimum of 4 in (100 mm) of knuckle clearance should be provided around all valve handwheels.

Valves should not be installed upside down.

Space should be provided for the removal of all valve internals.

توصياا لسالمة ال غيل :

-ال وصياا والطرق األتية ى أق ت . ل ى م اكل الصالاماا أث ات ال غيل :

صالاماا ال كم :

الل كم حيللث تكلوق ليقاق ت لغيلها ا و ل. رأ لل قلا م وأق تكلوق كلل ملن اما للورة لى أق تركلى صلالامااام صلة مبد لها ومبخرجها مس قيالة مساإة تعا ثالث أم ا قطرها عل األقل ل قليلل ء لطرا حركلة السلا ل

. ا ل الصالاد و ا مساإة الية عل ء قامة جواين ومسامري الفالن ة تسالك نفكها

Recommendations for Correct Operation : The following recommendations and methods should be observed to avoid valves problem du-ring operation :-

Control Valves : Control valves should be installed where their stems in a vertical upright position and a minimum of three diameter of straight pipe both in upstream and downstream of the valve to reduce the turbulence of the liquid in the valve and to get a straight space for removal of the flange studs or bolts.

5-5 Commissioning: 5-5-1 Pipework cleaning: Foreign particles in the pipeline can destroy valve seats and prevent movement of both plug and rotary valves, stopping them from sealing properly. If they are large enough, foreign bodies can completely block a control valve. Very small, hard

صدقة جاريه لروح من أعدهاللهم اجعل هذا العلم (170)

particles can cause rapid wear of the trim clearance. To prevent contamination problems it is necessary to clean all

pipework so that it is completely free of all loose weldsplatter , slag and other particles. Pipework and valves in solid handling systems should be cleaned to remove "out-of-spec" solids prior to commissioning. Gas and steam lines in particular, should be carefully cleaned by a series of blowouts, to remove scale and rust which could otherwise damage the valve. This is best done immediately afterpressure testing. The progress of the cleaning operation can be checked by blowing against an aluminum target plate. Systems handling flammable, hazardous or hygienic fluids may require purging of air before the piping can be vented and primed with process fluid. Nitrogen gas, distilled water or proprietary sterilising liquid may be required. Good piping design can ensure that pockets of air or contamination are not overlooked. Vent and drain valves at appropriate locations can indicate the progress of purge fluid. Leak testing of these types of system may be much more important than pressure testing.

5-5-2 Isolating valves: The seat tightness of isolating valves can be checked during purging, leak testing and pressure testing. The pressure decay of isolated pipe sections can be logged while connections and packing boxes are checked. Remember, accurate packing box leakage can only be measured when the pressurized fluid is very similar to the process fluid. Nitrogen leakage may not be very representative of the process gas leakage. Manual isolating valves should be operated using handwheel fitted to the valve. If leakage is more than expected/specified do not use cheater extensions. If, after inspection, the valve is found to be in good working order and still will not seal


properly the actuator mechanism or the valve style must be changed. Cheater bars strain and over-stress components and wear out valves very quickly. Power-operated isolating valves can have their operating mechanism checked without process fluid in the pipework. The control sequence and the travel limit stops can be verified. Ensure that close control signals actually close the valve. Also verify the effect of power failure and the Emergency Shut Down , ESD, signal when appropriate. The speed of operation of actuated valves can be very important for the stability of the process system. Valves which open or close too quickly can radiate pressure pulsations through the system. The effect of valve speed can only checked properly when the process fluid is pressurized and flowing at rated velocity. Power operated isolating valves should be set to operate as slowly as practicable .

5-5-3 Solenoid valves: Direct-operated solenoid valves can be commissioned without process fluid. Servo-operated solenoid valves require the process fluid to be present and pressurized for correct operation. Open and close signals should be checked for correct settings. The speed of valve operation may be important. Significant pressure pulsations may be created with larger valves. It may be possible to fit different springs to direct-operating valves so that the speed can be adjusted. Servo-operated valves have an orifice which can be changed to control the speed. In general terms, the slower the operating speed, the better. Some linear valves operate at very high speed for emergency isolation. These valves will cause severe pressure pulsations and vibration in piping systems which are long and/or of high velocity. Simulated operation for commissioning is best done with pressurised, stationary process fluid; this will avoid the


worst effects of the pressure pulsations. 5-5-4 Non-return valves: Non-return valves require flowing fluid for full commissioning. Adjustable valves can be set to open wide at maximum flow rate. When fitted, dampers or dashpots should be adjusted to provide an acceptable closing speed with minimum surge effects. It will be necessary to start and stop the fluid flow. This can take some considerable time with large systems. Listen to valves very carefully, with a stethoscope or screwdriver, while operating. It should be possible to hear doors swinging or chattering due to unstable stable flow conditions or vortices. Doors which move continuously during normal operation will tend to wear quickly. Stronger springs or a different spring rate may solve the problem.

5-5-5 Safety relief valves: Safety relief valves can be adjusted at site to optimize performance. If more than one valve is fitted, isolate all but one and commission in turn. The set pressure will have been fixed and checked by the manufacturer and the spring locked and sealed. Unless process requirements have changed there should be no need to adjust the set point. Many compressor and pump manufacturers set safety relief valves at + 10% whereas valve manufacturers prefer +25% because it allows the use of smaller valves. The set pressure for compressor/pump protection must not be reset higher without informing the compressor/ pump manufacturer. The set pressure can normally be adjusted up to 10% with one spring. Consult the valve manufacturer for adjustments over a wider range and for alternative springs. The set pressure should not be adjusted on-line. Serious accidents have occurred when safety relief valves have become unstable


resulting in very high operating pressures. Valves must be adjusted when unpressurised. Only adjust slightly between retries. The overpressure and blowdown can be adjusted during commissioning provided the operating and fluid conditions are suitable. Standard spring-loaded valves can only be optimized using a fluid which has very similar physical properties to the process fluid. Valves will have one or two adjustments to allow overpressure and blowdown to be set. Overpressure and blowdown can both be set with the safety relief valve on-line. The operating pressure should be less than 90% of the set pressure when adjustments are made. Set the overpressure first. Move the adjustment by one increment only between retries. Once the overpressure is acceptable, adjust the blowdown. Always replace or tighten locking devices during retries. Resetting the valve to extremes of operating conditions can result in unstable operation. When the line is clean, spool pieces can be removed and regulators/control valves can be installed. The valve(s) and gaskets should be an easy sliding fit into the gap in the pipe, and upstream and downstream pipes should be carefully aligned and concentric, and the flanges must be parallel. If these precautions are not observed and the pipes are pulled into alignment by bolting up to the valve body haphazardly, the resulting stresses will certainly cause the valve to leak and may cause it to stick or to fail prematurely in service. 5-5-6 Control valves and regulators: Regulators may be totally enclosed with the stem/spindle connection inaccessible without dismantling the valve. These regulators must be verified on the test stand before installation. Regulators of an open construction can be checked in a similar manner to control valves. Control valves should have been


fully checked before installation and it is important to check site records. The actuator and positioner, if fitted, should be disconnected and checked for full stroke. The air supply should be checked before connecting to the positioner. The positioner response to 0%, 25%, 50%, 75% and 100% signals should be measured. The positioner and actuator should be checked for air pressure failure response. If all is in order, reconnect the valve stem and recheck the stroking range. Regulators and control valves are frequently used in systems with compressors and pumps which create flow variations and pressure pulsations. Check the piping to see if dampers/filters specified have been fitted correctly and, when appropriate, are charged with nitrogen to the correct pressure. The nitrogen charge pressure, with the system at atmospheric pressure, should normally be 70% of the actual system operating pressure. Systems which operate over a significant range of pressures may require a different precharge setting. Initial commissioning may be performed with water, oil, air or nitrogen. Final commissioning and "fine tuning" can only be carried out when rated operating conditions with the proper process fluid are available. Final checks should include listening for flashing and cavitation. Both flashing and cavitation can create serious operating problems if overlooked during valve type selection and sizing. ****************************************************

6- Routine maintenance 6-1 Introduction: Regular maintenance operations will include external visual examinations, lubrication and packing adjustment. Staff must be aware of isolation and depressurization procedures before valves are dismantled. When necessary, decontamination facilities should be clearly available, not concealed at the back of the valve.


It is very important, particularly when using motor actuators with gate valves not primarily designed to be automatically actuated, that the valve gland and the drive-nut are effectively lubricated all times. If necessary extra lubricators should be fitted. Valves handling volatile organic compounds, VOCs, or hazardous fluids should have the packing box leakage checked regularly. Some compounds will be regulated by health or environmental legislation. Valves for hazardous or controlled fluids should have sampling ports on the packing box for portable or continuous monitoring. A leakage log for these valves is essential to predict repacking dates. Some valves are installed but are required to operate or move infrequently. In these situations valves can present seat and spindle/stem sealing problems. The working environment should have been considered during valve type selection, but the ideal valve may not be able to cope perfectly with the operational requirements. The routine maintenance for such valves should include:

Spindle/stem movement.

Packing lubrication and adjustment.

Seat/plug inspection and relapping. Many sub-contract organizations offer valve maintenance. Routine maintenance, at scheduled times, is very easy to implement as is a major overhaul at annual plant shutdowns. Unscheduled maintenance, such as a service crew passing a valve on the way to another job or called out for emergencies, is more difficult. If a sub-contract maintenance agreement is considered then the use of a local organization is preferable. Clearly, agreement on rapid response and standard fees must be secured before contracts are awarded. The staff, facilities and quality assurance programs of subcontract organizations must be fully investigated. Factory trained personnel are essential for complicated valves. High quality machine tools, welding and inspection equipment are

من أعدهاللهم اجعل هذا العلم صدقة جاريه لروح (176)

necessary for good repair work. The limitations of test equipment must be known before valves are committed for repair. A strict quality assurance program must be running effectively to ensure all aspects of maintenance and testing achieve the desired objectives. Staff, at all levels, must have very broad engineering experience. The valve user must be able to quantify the faults and provide acceptance levels for the repairs. Numerical, measurable values must be assigned to important variables. Written descriptions, rather than numerical values, are subject to interpretation. For example: *"The valve stem in contact with the packing shall be smooth"-is a poor requirement. *"The valve stem in contact with the packing shall have a surface finish between 0.8 and 0.4pm"- is precise and verifiable. When requirements are poorly defined the end result can be less than satisfactory. A review of the sub-contractor's quality manual will indicate the range of quality levels available for specific tasks, if a subcontractor cannot meet the quality level for a task then a quotation is unnecessary. Quotations for repair of major valves must be accompanied by an itemized list of operations with associated inspection/quality controls. Extra special attention must be given to the reclamation of worn components by plating, welding or metal spraying. Treatments prohibited on the new valve components should not be allowed during repair. Impregnation of porous castings is frequently prohibited for new valves; there is no sound reason why it should be acceptable as a repair. Some organizations win contracts by quoting low prices. The contract value is subsequently increased by extras for unexpected work. Maintenance quotations for major valves must include a list of extra costs which covers probable additional work. Extras from the list are then the only


additions to the contract considered. Competitive quotations can then be reviewed on a "total" cost basis and so enable repairs rather than replacement to be justified. The routine maintenance system for safety equipment must operate independently from other maintenance functions. Safety checks, to comply with pressure codes or operating licences, must be performed at prescribed times and cannot be delayed by other jobs. Inspection and maintenance of safety systems must be allocated a much higher priority than other tasks. Environmental health or pollution inspectors can shut down processes, if legal requirements have not been met. Computerized management systems can prompt personnel to carry out routine inspections and testing. It is essential to keep very good records of inspection, tests, overhauls, parts failures and replacements. Specialist companies can offer on-line testing of safety relief valves. The valve is lifted manually, pneumatically or hydraulically to confirm full travel and the capacity. This type of testing is questioned by some valve manufacturers who think it to be inaccurate. It is best to seek the manufacturer's advice before committing contracts. On-line testing of this type may not be acceptable for code or licensing compliance. In any event, on-line testing does not replace routine, regular strip-downs and physical inspection. Some process systems may require periodic pressure testing to comply with construction codes or legal requirements. The process will have to be shut down to perform the pressure test and the opportunity should be exploited to carry out inspections of critical equipment.

6-2 Reconditioning Nozzles And Discs: Safety relief valves fall into the category of very infrequent operation. They are fitted as a safety system and should not form part of normal control operations. Equipment or


machinery operation should not require them to be lifted routinely. Safety relief valves should be used as dedicated safety devices. Safety relief valves that have lift levers which have not operated, should be lifted manually on a regular basis, therefore check the equipment manufacturer's instructions. Valves should be lifted at least three times a year; some compressor manufacturers recommend once a week. Another recommendation is based on set pressure: * Below 70barg: lift once a week. * Above 70 barg: once a year. This last range, however, seems to be illogical. Nozzles and discs will wear, become eroded or corroded and the safety relief valve will leak. The seat seal must be maintained to ensure proper valve operation. Unless the seat surfaces have been damaged, regular lapping should ensure proper valve operation and good sealing. The seating surfaces are perfectly flat and must be true without irregularities. ANSI/API 527 specifies a surface flatness of within 0.51μm. Standard production methods achieve flatness within 0.025 to 0.3pm. The nozzle and disc should not be lapped against each other but individually against a lapping block. If a disc insert is fitted the insert must be removed for lapping. Safety relief valves that have balance bellows should be dismantled with great care. Damaging the bellows during routine maintenance may prove a costly mistake. Measure and note the position of the spring adjuster prior to dismantling. Very clean working conditions are necessary for successful lapping. A cast iron or plate glass lapping block can be used for all circular seating. One side should be used for rough lapping and the other for polishing. Select the "truest" side for polishing.


After rough lapping, the nozzle and disc should be polished with the finest compound available. When finished, the seating surfaces should have an even matt finish. If only the nozzle requires lapping, this can be performed in situ once the top works have been removed. Some applications may require the seating surfaces to be "super-finished" with diamond compound. A dedicated lapping block must be used for this purpose. Some diamond compounds require special thinners; always ensure a supply is available before starting. When nozzles or discs are badly scratched they must be machined prior to lapping. Nozzles can be machined in situ with a portable machine. When set up properly this is the most accurate method of machining. Standard tools can be used for globe valves as well as safety relief valves. Nozzles can also be machined in a centre lathe. The nozzle can be machined assembled in the body or independently. In either case the set up must be perfectly "true" before starting. Nozzles should be removed by using the tool provided by the manufacturer. If they are tight or seized in with sediment /corrosion, release oil should be tried. If unsuccessful, gentle heating of the body may assist. Discs can be machined in a centre lathe but may be very difficult to grip. Some designs may have centers for machining between centers; this is the easiest option. Again, accurate setting up is essential. Some safety relief valve manufacturers provide remachining drawings showing the new profile and limits of wear. Tools should be ground to the valve manufacturer's instructions and lapped with an oil stone if necessary. Very rigid tooling is essential to produce a smooth finish on the tough materials used. Lap and polish the surfaces before reassembly.

وح من أعدهاللهم اجعل هذا العلم صدقة جاريه لر (180)

Some safety relief valves include an elastomer seal in the disc or piston to provide good seat tightness. The seal must be inspected regularly for the low leakage to be maintained. Pilot operated valves have moving parts and seals, and possibly diaphragms, in the pilot assembly. The pilot assembly must be inspected and maintained regularly if the benefits of the pilot system are to be achieved.All components must be thoroughly cleaned prior to reassembly. It is essential that all traces of lapping/polishing compound are removed. If the spindle has been polished with emery tape, then all traces of emery dust must be removed. Failure to clean parts thoroughly, which have been lapped or polished , will result in rapid wear and loss of seat seal. Sliding bearing surfaces should be lightly lubricated with a lubricant suitable for the service conditions. If the nozzle or disc has been machined, the assembled valve should be tested and reset before returning to production. When servicing regulators and control valves it is obviously important that the maintenance engineer understands how the valve is constructed and operates. Without such knowledge there is a risk that equipment may be damaged, and worse, that serious damage could be caused to a complete process, with all the consequences of plant shutdown. All regulator and control valve actuators must be able to react to even small variations in input signal. Any lack of performance is usually obvious from a recorder chart reading of the controlled variable. Before servicing, however, it is important to ensure that the process or the valve is isolated and by-passed, if the repair can be undertaken in situ ,e.g., the "stroking" of a valve positioner.


If the valve has to be removed from the line, it is usual to do this under a "permit-to-work" system that ensures that the valve is drained or vented and decontaminated of toxic or corrosive substances, before it is removed from site to the workshop area. Large companies usually carry out their own preventative maintenance program. They have an established routine for inspection of all larger components as well as the replacement of packing, "O-"rings, seals, diaphragms and other non metallic materials. The advice given in Sections 2 to 6 applies to normal maintenance repairs and includes some general instructions on how the work should be carried out. Remember, there are usually specific manufacturers' instructions which must be made available and followed. If there are a large number of regulator and control valves to be serviced, it may be worthwhile engaging a specialist contractor. Most of the larger manufacturers listed in the Buyers' Guide in Chapter 21 have service departments, service centers or agents that specialize in the overhaul of valves. It is also possible to arrange some expert training of staff, who should then be in a position to undertake regular maintenance or cope with breakdowns with greater confidence. The training should include instruction on how to remove, refit and overhaul an actuator, how to remove a gland packing and repack the box, and how to adjust the stroke of a valve, with or without a valve positioner.

6-3 Replacing Actuator Diaphragms: Before attempting to renew an actuator diaphragm, the compression of the spring should be relieved as much as possible by releasing the spring adjuster. Then two, and only two, of the bolts on opposite sides, holding together the


diaphragm chamber, should be replaced by long studs which are fitted with nuts. These should be done up tightly to hold the housing together while the remaining bolts are being removed. When this has been completed, the stud nuts can be slowly released and the diaphragm housing should come apart. Then remove the upper casing from the actuator housing. In the case of direct-acting diaphragms, see Figure 74, the diaphragm can be lifted directly and replaced with a new one.

Figure 74: A direct-acting diaphragm actuator


On reverse-acting actuators, see Figure 75, the actuator housing must be disassembled to gain access to the diaphragm.

Figure 75: A reverse-acting diaphragm actuator

Most actuators have an injection molded diaphragm, the profile of which ensures that the surface area remains as constant as possible throughout the valve travel. Suitable replacement diaphragms for the range of standard actuators should be held in the users' stores. When the actuator is reassembled, the bolts should be tightened evenly. Check for leakage by using soapy water or a proprietary aerosol.


6-4 Replacing seat rings: There are two main types of seat rings in regulators and control valves:

Cage-guided valves where the seat is retained by the cage.

Screwed-in seat rings. The first type presents no problem. For screwed-in seat rings, the procedure is as follows: 6-4-1 Select an extractor of the correct size. 6-4-2 Fit the correct number of spacer rings to keep the seat lug bar down. 6-4-3 If the seat cannot be loosened by using the standard turning bar, see Figure 76 , then it is permissible to add a

Figure 76: Correct use of the seat ring extractor

العلم صدقة جاريه لروح من أعدهاللهم اجعل هذا (185)

length of pipe to obtain more torque whilst tapping the drive wrench, lightly, with a hammer. Stubborn seats may need to be soaked with release oil for a couple of hours. 6-4-4 Before screwing in the new seat ring, the threads must be cleaned thoroughly and degreased before thread paste can be applied. 6-4-5 Tighten the new seat ring using the extractor that was used for removing the old seat. NOTE: Some seat rings are "tack-welded" to the valve body. This weld must be removed and release oil applied before any attempt is made to unscrew the seat using a seat ring extractor. These extractors can be purchased from the valve manufacturer.

6-5 Grinding of valve seats: Some leakage at the valve seat with a metal-to-metal contact with the plug must be expected. There are varying leakage requirements specified according to class, which differ in the quantity of leakage under test conditions. If the leakage is unacceptable, then the plug must be ground to the seat using a good quality grinding paste. Using a "lift and twist" motion prevents the metal surfaces from scoring each other in case the grinding paste is removed from the surfaces. During this operation the weight of the plug should be supported as appropriate. To obtain a good grip and good guiding of the valve plug, a special tool should be made and grinding should be carried out with the packing box and packing fitted to the valve body. On no account should any gripping tools be applied to the valve stem, see Figure 77. For double-seated valves, where one seat may be ground-in before the other, polishing paste should be applied to the fin-


ished seat whilst grinding the other seat. Never allow one seat to be without polishing paste while grinding the other. More serious damage cannot, however, be ground out in this way, but must be repaired by machining. Portable pneumatic and electric machines can be rented. Alternatively, specialist machining companies are able to visit the site and refurbish valves in situ.

Figure 77: Typical set up for valve plug/seat grinding

6-6 Adjusting the stem connector: 6-6-1 Linear valves: 1- Remove the stem connector and push down the valve stem

أعدهاللهم اجعل هذا العلم صدقة جاريه لروح من (187)

to close the valve. Ensure that the valve plug is in the closed position - i.e., the seat and plug are in contact with each other, see Figure 78. 2- Set the actuator in its corresponding closed position: For direct-acting actuators, the valve stroke is downwards from the upper position. For reverse-acting valves, the closed position is as it is in the loosely attached position. 3- Move the actuator stem about 2mm closer to the valve stem and connect both stems by means of the stem connector.

Figure 78: Valve and actuator stem connection


4 -Check that the actuator can travel its full stroke. Make sure that the plug touches the seat before the actuator comes, to its limit. Minor adjustments, less than 2mm, can be made by screwing the stem connector slightly, after loosening the cap screws which hold it together. 5- When everything is connected together, screw the indicator plate into a position which corresponds with the valve in closed position. 6- Using a gauge connected to the actuator signal input and a dial gauge on the valve stem, set the valve according to the specification plate.

Figure 79: Actuator mounting positions

6-6-2 Rotary valves: Rotary valves and actuators can be assembled together in many ways, as shown in Figures 79 and 80. The most common alternatives are with the actuator mounted either to the left or to the right with a choice of which direction the valve should travel in the event of air failure.


Valves of this type are usually fitted with direct-actoin actuators and the arrangement for valve opening or closing in the event of air failure is made by changing the connection between the valve spindle and lever. In the case of ball valves, virtually any connection point on the valve spindle is ideal provided fine adjustment can be made with the actuator stem. Fine adjustment on rotary valves can only be made while the

Figure 80: Notation for actuator mounting position

Figure 81 :Butterfly valve disc position relative to valve bore


valve is not being used in the process, since it must be possible to measure the position of the disc relative to the bore of the valve body in order to check that the disc is positioned correctly, see Figure 81.

6-7 Packing boxes: Packing boxes can suffer severe local damage due to wire drawing. Portable machines can be hired to remachine the packing box in situation. This facility can be extremely useful for large valves in locations which present dismantling problems.

6-7-1 Routine packing adjustment: With the exception of chevron packing rings, see Figure 82, all packing types are compressed by means of the packing box nuts. This adjustment is extremely critical and can, if not carried out correctly, damage the valve before the process is even started. It is advisable to delegate the job of "running-in" the packing boxes to one person, whereby the packing are compressed in small stages - one third of a turn of the packing box nuts during a period of several hours, until the valves stop leaking, without causing unnecessary stem friction. Fig 82: Chevron packing rings


The packing box can be likened to a bicycle tyre inner tube, which bursts if it is overloaded. The packing must remain soft in order to follow the movement of the stem. It must retain its sealing qualities and must not be overloaded by over tightening the packing box nuts. 6-7-2 Replacing spindle/stem packing: The packing around the valve spindle/stem should be replaced if leakage continues, even after adjustment. Packing can also be replaced while carrying out other service work. Chevron rings should be replaced completely when they leak. Check that there is no pressure in the system before removing any packing. If the packing is of the split type, it is possible to remove it without removing the actuator, but this can easily lead to irreparable damage to the spindle/stem and stuffing box surfaces, unless the proper packing extractor is used. Do not attempt to remove packing by applying pressure through the lubrication nipple. This can be dangerous and does not usually work, since in most valves one half of the packing is below the lubricating connection. The following procedure is recommended":- 1)Consult manufacturer's instructions a day before repacking is scheduled. It may be recommended to soak the packing rings in light oil overnight before fitting. 2)Check the availability of approved lubricants and cleaning solvents for biotechnical and hygienic applications. Disconnect the valve stem from the stem connector. 3) Remove the actuator from the valve body. 4) Remove the bonnet and pull out the plug and stem. 5)Insert a copper drift, slightly larger in diameter than the stem, through the bottom of the bonnet and push out the old packing. Use a proprietary packing extractor, shaped somewhat like a flexible corkscrew, to remove the old packing. Discard the old gland packing. If the replacement


packing is in the form of chevron rings, check that the original springs and headers are serviceable and in place before fitting the new packing rings. These should be lightly lubricated to assist assembly. 6)Clean the bonnet and packing box and inspect the spindle/ stem. There may be scratches or burrs which can damage the new packing. Spindles and stems that seal against PTFE chevron rings are usually honed to a super finish and must be free from damage of any kind. NOTE" Never apply tools directly to a valve stem. 7)Check the valve plug, the seat ring and other parts of the valve trim. 8)Reassemble the valve body and fit the bonnet. 9)Assemble the valve body and bonnet in the same way as described in connection with connecting the flanges. 10)Push in the packing rings one by one in the correct order. Use silicone grease, or approved hygienic quality grease, on PTFE packing rings and make sure that they are not damaged by the spindle/stem threads. For compressed fiber rings fitted to linear control valves, and for all rings fitted to rotary valves, it is essential that each ring should fit the gap between the spindle/stem and the packing box accurately. Because these packing are energized by fluid pressure alone, there is more friction between the ring and the sealing surfaces. So unless gland is very carefully assembled, the rings will not "bottom" in the box. It is not good enough to fit the gland follower and to drive the packing to the bottom of the box. This simply does not work, and leads, because the bottom ring is not properly supported, to rapid failure of the packing in service. The only correct way of fitting packing rings of this type, is to measure the depth of the box with a depth gauge and fit each ring separately with the aid of a copper drift. When the first ring has bottomed this should be confirmed by checking with the depth gauge. The


second and any subsequent rings are fitted in like manner. The procedure takes rather longer to read about than it does to carry out, but it has been proven time and again in practice, on valves that were once considered difficult, e.g., large butterfly valves on medium and high pressure steam duty. 11)Fit the components which compress the packing. 12)For PTFE packing rings, the gland nuts should be tightened fully; for other packing types, the nuts should only be tightened sufficiently to prevent leakage. 13 )Fit the actuator.

Figure 83 :A typical parts list

6-8 Spare parts: Equipment and valve manufacturers invest considerable sums

لروح من أعدهاللهم اجعل هذا العلم صدقة جاريه (194)

of money in designing and developing their products. Spare parts are manufactured to the same standard as the new, complete equipment. The sale of spare parts forms an integral part of a manufacturer's income. Small machine shops can easily copy the physical dimensions of a component, but complete "reverse engineering" is impossible. They do not have research and development departments supporting them. Short-term cost reductions can lead to major cost expenditure when copied parts fail catastrophically and damage other components. Original equipment manufacturers guarantee their spare parts . Guarantees and warranties for the valve itself will normally be invalidated if parts, made by others, are used. Spares should always be ordered from the original manufacturer of the valve. When ordering spare parts, always state the following:

Valve model.

Valve serial number.

Year of manufacture.

Part number and material.

Part reference from spare parts list, see Figure 83.

Quantity.

Your valve tag number. When ordering spares for special valves it may be very helpful to include all the data given on the nameplate or a copy of the valve data sheet. During the manufacturing phase of special valves, a quotation should have been obtained for routine and special spare parts. The quotation would indicate the lead time of any parts which would have to be specifically manufactured. This information should be stored with the other valve data for easy reference.

***************************************** لهم اجعل هذا العلم صدقة جاريه لروح من أعدهال (195)

7- Trouble-shooting When operating problems arise at site, it is not necessarily a valve problem. Calling out a service engineer can be costly when the fault is found to be incorrect installation or "incorrect" operating conditions. The following logical approach can be used initially for all valve types.

Check the installation: * Was the valve commissioned successfully? * Is the valve the right way round? * Is the valve in an acceptable orientation? * Does the valve move freely? *Is there any build-up of dirt/wax/corrosion products restricting travel? * Is all ancillary equipment fitted? * Is all pipework connected to the correct ports? * Check for leaks. *Are the electrics wired correctly? *Are electric motors running in the correct direction? * Is automatic control overridden by local settings? * Have any safety devices tripped? *Has the valve been serviced recently? * Have flanged connections been tightened up evenly? * Are relevant filters and orifices clean? *Are springs intact? *If pulsation dampers or accumulators are fitted check gas precharge pressures.

Check the operating conditions: *Has the valve ever operated successfully? * Has the valve been operating under data sheet-defined conditions? *Check operating logs for historical data. * Is a valve used continuously rated "continuous" or "intermittent"? *Has there been a recent process upset?


* If instrumentation indicates the valve has always operated Within the defined conditions, check when the instruments were last calibrated. Recalibrate if necessary, but note errors and apply to most recent operating conditions.

Actions: *If installation is correct and operation is within prescribed Data sheet limits, read the following paragraphs and the manufacturer's trouble-shooting guide; request a service engineer if problems cannot be resolved. * If operation is outside prescribed data sheet limits, read the manufacturer's product specification for absolute operational limits. If the valve is unsuitable, check for upgrades or replacement. Most valves are designed to contain pressurized fluid. Leaks of escaping fluid are relatively easy to detect. Leaks on valves in vacuum services may be much harder to find and so specialist ultrasonic sensors may be necessary. Process and equipment engineers frequently incorporate safety margins within the operating parameters specified. Adding a percentage to operating pressures ensures that compressors and pumps can cope with all realistic conditions. Equipment manufacturers frown on this practice and would prefer actual conditions to be specified and a safety margin indicated separately. Safety relief valves, regulators and control valves can be undersized by using higher pressures for selection than experienced in normal operation. Process designers and contractors sometimes overlook trace elements and the possibility of small quantities of solids in process streams. Undocumented trace elements can cause severe corrosion problems which result in: *Packing degradation and fugitive emissions. * Gasket failure and leaks. *Diaphragm or bellows failure. *Seat corrosion and loss of seal.


*Body corrosion and loss of pressure containment. Unexpected fluid attack and corrosion can cause major operational problems. Very small quantities of abrasive solids can cause rapid valve wear. Research has shown that 0.25% of solids, similar to fine sand, can double the seat/plug wear rate. The wear rate caused by entrained solids is a function of velocity raised to a power of between 2.5 and 5. Small increases in velocity can result in large increases in erosion. Safety relief valves, regulators and control valves, and valves which are liable to operate with high fluid velocities, will be very susceptible to erosion caused by solids. Erosion can result in: *Spindle/stem wear leading to packing leakage. *Spindle/stem wear leading to spindle/stem failure. *Seat/plug wear leading to leakage. *Seat/plug wear leading to loss of control. *Diaphragm wear leading to loss of control. *Body wear and loss of pressure containment. Erosion can be alleviated by the use of very hard materials and surface coatings. Hardenable stainless steels, such as 17-4PH and 440C, can be heat treated to resist erosion. Soft metals can be coated with glass, Stellite TM, tungsten carbide or ceramic. If solids are specified initially, alloy cast irons can replace soft materials such as carbon steel. Erosion can produce an increase in corrosion indirectly; erosion corrosion. Mild erosion can remove the protective oxide layer from corrosion resistant materials. Clean metal may be easily attacked by the process fluid. The oxide layer is not allowed to repair itself due to the erosive action of the solids. Rapid material loss ensues. Mild cavitation can produce similar effects to erosion corrosion. The cavitation implosions remove the protective oxide layer and the corrosive fluid elements remove bulk material. Fully developed cavitation removes the bulk


material directly. If the cavitation bubbles implode next to a solid surface, bulk material is plucked from the surface due to the extremely high local pressures created. Cavitation damage has a characteristic "popmarked" appearance and is usually easy to identify. Entrained gases in liquid, flashing and cavitation cause a reduction in flow capacity of all liquid valves. The volume of gas/vapor replaces liquid of a much higher density and consequently the mass flow for a given differential pressure is reduced. Flashing and cavitation can be expected in some liquid applications and should have been considered during valve type selection and sizing. Unexpected flashing and cavitation can effectively undersize valves, creating a flow restriction. Process designers and contractors sometimes omit to quantify entrained gas and vapour in liquid streams. The expansion of gas and vapour can create choked flow conditions, restricting mass flow, due to the pressure drop across a valve. Pressure pulsations, vibration and thermal shock can create very serious operational problems. Equipment and valve ratings are based on steady-state operating conditions. Steadystate is defined as all relevant parts of the valve being at the same temperature, pressure and when appropriate, velocity. Pressure pulsations and vibration can cause rapid wear in some valves. Valves with loose handwheels and pressure gauges with broken pointers are commonplace. There is an allowable residual pressure pulsations , if the valve is subjected to higher pulsation the manufacturer should be consulted. This information provides guidance eliminating excessive piping vibration in petrochemical installations. Lightweight stainless steel systems for hygienic applications should use rather lower pulsation values. Both pressure pulsations and vibration cause moving parts to rattle within their clearances. The continuous movement of


parts creates wear, which increases the clearance, which increases the wear rate. Correct valve type selection is the key to the solution but the problem must be recognized at the design stage. Changing the valve type, when possible, may be the only solution. The mild effects of thermal shock are seizure and jamming. The internal components expand much faster than the guides and pressure containment, and the valve locks up. If valve movement is not forced, the valve will return to normal operation once temperatures have equalized. If the valve is forced, permanent damage may result. The most serious effects of thermal shock are cracking of the pressure containment and the failure of gaskets and seals. If process temperatures change by more than 4o C per minute thermal shock problems are a possibility. Valves can jam due to slow temperature changes when warmed up properly. Valves which are wide open or closed can suffer from differential expansion problems. All components are warmed, or cooled, slowly to avoid thermal shock but internal clearances of the stem are removed due to the end of travel. Differential expansion/contraction rates result in high tensile/ Compressive forces being induced in the stem. Linear motion valves are the most common, but butterfly valves can be jammed closed depending upon the seat design. If temperatures are returned to the original value when the valve was opened/closed, normal operation should be possible. When process temperatures vary considerably from shutdown, valves should not be opened wide and sealed on the back seat. The valve can always be opened further while operating. Solenoid valves are usually designed for clean fluids. Traces of solids may accumulate and prevent full opening or closing.

العلم صدقة جاريه لروح من أعدهاللهم اجعل هذا (200)

If the solids cannot be filtered out, then the valve must be cleaned regularly.

Table28 :Typical spring-loaded safety relief valve problems


Spring-loaded safety relief valves, can suffer from chattering, fluttering and instability of operating conditions including low or high popping pressure. Table 28 outlines typical causes. Safety relief valves used in steam applications can be very problematic and the manufacturer should be consulted. Regulators and control valves are frequently used in systems with compressors and pumps which create flow variations and pressure pulsations. Control instability can be caused by undamped pulsations, therefore piping must be checked for correct fitting of dampers/filters and correct gas precharge of bladed diaphragm devices. for continuous operation at 120o C Intermittent operation up to 200o C is possible with some. Non-metallic valve materials can be repaired. As with metallic materials, the exact specification of the material must be known before any repair can be contemplated. Typical repair techniques include: *Solvent welding. *Thermal fusion welding. *Reinforced adhesive. Patches can be constructed with adhesive and reinforced with metal mesh or glass-fiber ribbon. Whenever possible, trials with solvents and adhesives should be conducted to test the bond strength and the effect of the process fluid. NOTE: When repairs are made in a material which is different from that of the component, the difference in thermal expansion should be considered. Slight changes in temperature may overstress the bond and result in delamination.

***************************************** (202) اللهم اجعل هذا العلم صدقة جاريه لروح من أعده

8- Valve Selection

The following are the steps to arrive at the most suitable

selection of the valve taking into consideration the life span

expected and cost involved.

عة وال كلفلة لوصو ءك أإول ء يار م ا ى للصالاد م. األ ذ ا ا ع ار إجة اخلدمة ام وقاإيالا يل طواا ال املة و

اخلطوة األوك ه ضديد نوعية الصالاد ء ا ماكاق للع أو ءيقاف ال دإق, اخل ق, فيف الوغن, تغيري ا ىاه مث يلار ال لوع ام ا لى إلإ ا وجلد أك لر ملن نلوع م ا لى ىلرر مقارنلة ل فوليل أحسل ها و (4)ء خداد اجللدو

راشة ك رية القطلر مفوللة علن صلالاماا ال وانلة كصلالاماا ءيقلاف لل لدإق ا وعل يل ام ا إإق صالاماا الف طوط الوغن ام خفض و رجة احلرارة ام خفوة ا ش كاا تشيد امياه نس ى ءع اراا احل م والوزق وام غل

وال كلفة و

الصلالاماا قلد نعلضو , اخلطوة ال انية ه ضديد مقلااب الصلالاد وهلو علا ة نفلس قطلر اما لورة امركلى عليهلا -ت ج مبقا اا الف امقااب امطلو أوأً ت واإر ا السوق إيالكن ء خداد مقا اا أكلش أو أصلغر ماملا أ

يس ى ل م كلة حي أو تكلفة او مترير لفرش ال ظيف او الف صو

The first step is to determine the valve type: isolation /

stopping, throttling, pressure release, directional change, then

use the table (29) to select the suitable type, if there are more

than one suitable type, a comparison should be performed to

differentiate the best one, for example, large-size butterfly

valves are preferred to large-size gate valves as stop valves in

low-pressure and low-temperature cooling water systems, due

to space, weight, actuator, and cost consideration.

- The second step is to determine the valve size which is usually the same of the pipe size, some valve may not be manufactured in the required size or not available in the market, smaller or larger size can be used if this doesn’t ca-use a problem about the space or the cost or line pigging.


Table29: Valve types and typical applications

اخلطللوة ال ال للة هلل ء يللار شللكل أمللراف الصللالاد إفلل طللوط السللوا ل تفوللل الفالن للاا ولكللن ا الغللازاا تفوللل األملللراف الكانللل لل لللاد ولكللن يفولللل الرجللوع ءك الكلللو امعللن ابلظلللروف اموجللو ة ملللن حيللث احل لللم

وع للدما يكللوق اخلريللر و أديللة إقللد مي لل. ء لل خداد الوصللالا والوللغن و رجللة احلللرارة ومللا ة تصلل ي. الصللالاد و و امقلوتة , وقد تس خدد الفالن اا العازلة م . ال آكل اجللفاىن نني الصالاد وإالن اا اخلن

اخلطوة الرانعة ه ء يار اما ة ام ا ل ة ل صل ي. الصلالاد وإقلاً و لواص املا ة أو الو لن امسل خدد لله الصلالاد -املوا الالمعدنيلة والصللى اللذر أ يصلدأ الصللى الكرنلوىن ، رارة ال غيل وميكلن ء ل خداد رجة حو و غن

والس ا عالية اجلو ة ا تص ي. أج ات الصالاماا و اللىت حيلد Mss-sp-61 ,API 598اخلطلوة اخلامسلة هل مراجعلة ال وصليف القيا ل امسل خدد م لل -

ار ا الورشة و أث ات ا ال سر امق و ع دما يكوق الصالاد مغلقاً ى حللو للاق الصللالاد م لل. للو اهلللوات ءك الصللالاد ا حللاأا للاخلطللوة السا للة هلل ء يللار احل للو ام ا -

. للخللارج نسلل ى الوللغن الللداخلل وميكللن ء لل خداد مللا ة ال يفلللوق لل للو لخلللة الوللغن أو تسللر امللاح و اجلراإي لدرجاا احلرارة األعل ملن لل كالا يس خدد ، رجة إهرهني °400لدرجاا احلرارة حىت

وا ا خداماا ال ار ة جداً ى محاية احل و من ال المس م. اما ة ال ار ة و اخلطللوة السللانعة هلل أق يراعلل امصللالم تللرك حيلل م ا للى حللو الصللالاد للوصللو ءليلله وءجللرات الفلل والجكيللى -

طللاا اا اخلدمللة الطويلللة للى ء يللار صللالاماا أ ض للاج ءك و وا ا ااوالصلليانة الدوريللة وءجللرات ا صللالح يي و صياتا ورية اب ات عاللياا ء دا احل و وال

اخلطلللوة ال ام لللة هللل ءجلللرات مقارنلللة يلللار ال كلفلللة ال الو جيلللة مللل. مراعلللاة أق الصلللالاماا الر يصلللة ض لللاج ءك -كلفة ت غيل أعل ( و ومراعاة أيواً اق ال كلفة العالية ءصالحاا أو ء داأا ورية للصالاماا أو أج ا ها )ت

قد تكوق مرإو ة من جانى ام جر و اللهم اجعل هذا العلم صدقة جاريه لروح من أعده (204)

مللاتيك إللإ ا كللاق كللذل إي للى األ للذ ا و اخلطللوة ال ا للعة هلل ضديللد ء ا مللا كللاق الصللالاد حي للاج ءك م للغل أوت -لصلالاد ع لد ءنقطلاع مصلدر أي لذه ااإ. اموجلو ة ابموقل. ارة ام لغل والو ل. اللذر ا ع ار ال سهيالا وام ل

الطاقة قد ميل عل امصالم ء يار نوعية حمد ة و

The third step is to select the valve-end connection, in liquids service, flanged connections are preferred, but in gases the welded connections are preferred, but it is preferable to check code requirements concerning the mention piping system condition such as size, pressure temperature, and material of construction. When leakage through joints is a concern, threaded joints may be prohibited or limited. Insulation flanges may be needed to prevent galvanic corrosion between the valve and pipe flanges.

- The fourth step is to select the suitable material according to

the medium characteristics, opera-ting pressure and

temperature, carbon steel, nonmetallic, stainless steel, and

high-alloy may be utilized in manufacturing valve parts.

- The fifth step is to check the applicable standard such as Mss sp-61 and API 598 which specify the acceptable seat leakage when the valve is closed and tested in the shop.

- The sixth step is to select the suitable stem packing to

prevent inward air leakage in vacuum condition or outward

fluid leakage in pressure condition. Inverted-V Teflon packing

may be used to temperatures up to 400°F, graphite packing is

used for higher temperatures. In cryogenic service, packing

must be protected against the contact with fluid.

- The seventh step is, the plant designer must provide a space

for access, assembly, and disassembly of the valve to

facilitate maintenance and repair works. In long life plants,

the valve must not require frequent maintenance except the

replacement of packing or lubrication.

- The eight step is to make a compromise to choose the


- optimal cost, the low initial cost valve will need frequent

repairs or replacements of the valve or valve parts (higher

running cost), high initial cost valve may be prohibitive.

- The ninth step is to determine if the valve requires an

actuator, if needed, keep in mind the available facilities and

utilities at the site, desi-red failure mode will dictate the type

of the ac-tuator

*****************************************

9- Flow Through Valves

ال دإق عش الصالاماا :

: (K)معامل ا ح كاك

K كاليلية ل كاا األتنيى لجرات ىار لل صو عل معامل ا ح كاك عا ة ما يقود صانع امس ل ماا اللكل م ها ك س ة نني قيالة ا خنفاض ا الوغن عش اجل ت ونني ماقلة احلركلة للاللا . ع لدما يعلش هلذا اجلل ت وميكلن

-حسانه من امعا لة األتية :

Friction factor coefficient (K) :

Usually, manufacturers of piping fittings perform experiments to get the fitting friction factor or resistance coefficient (K) as a ratio between the pressure drop through the fitting and the kinetic energy of the fluid when it passes the fitting it can be calculated from the following equation.


ويع ش معامل ا ح كاك مسة من مساا الوصالا ال كاليلية للخطوط الىت تساعد امصالم ا حسا الفواقد الكلية ا ش كاا األتنيى و

نطلو مكلاا ملن اخللن امركلى عليله ويقود نعلض الصل اع ابل ع لري علن إواقلد ا ح كلاك لال الوصللة ال كاليليلة اجل ت ي س ى ا نفس الفواقد الىت حيدثها هذا اجل ت و

-كالا يل : Kوا حالة ال دإق عش الصالاماا حيسى معامل ا ح كاك ●●

This K factor is a feature of the fitting which helps designer to

calculate the total friction in the piping system.

Some manufacturers define fitting friction loss as an

equivalent length of an actual straight pipe having the same

fitting diameter.

●● In case of flow through valves, K factor is calculated as

follows :-

طة صانع الصالاماا لف اا خم لفة للصالاد تع الد نصورة ك رية عل عاللياً نوا Kوي م ء ا معامل ا ح كاك كالا هو مو ك ا ال و األتية ال س ة امئوية م وار إ ك الساق من و . الغلق ءك ام وار الكامل للف ك

K factor is found experimentally by the valve ma-nufacturer

for different valve openings, it depends greatly on % age of

valve opening as it is shown in the following items :-


-: CVمعامل ال دإق

ف °60ابجلللالوق األمريكلل / قيقللة مللن امللات ع للد QOع للارة عللن معللد ال للدإق ابلصللالاد CVمعامللل ال للدإق لف ة حمد ه و 2يكوق إاقد الوغن عش الصالاد واحد ابوند/نوصةع دما

Flow Coefficient CV :

There is flow coefficient CV states the flow capacity of a valve

QO in gal (US) / min of water at a temperature of 60 °F that

will flow through the valve with a pressure loss of one Ib/in2

at a specific opening position (use QO / Q = VO / V and

definition of CV).


إاقد الوغن اخلانق :

ولكلن ع لد ع دما ي ا إرق الوغن عل مرا الصالاد إإق معد ال لدإق علش الصلالاد لوف يل ا ت علاً للذل الوصللو ءك إللرق للغن معللني )إاقللد للغن( إللإق أر زاي اا ا إللرق الوللغن للوف أ تلل ر ءك زاي ة معللد ال دإق ن ي ة ل أثري ال كهف ا السوا ل و رعة الصوا ا الغازاا وهذا الفاقد ا الوغن يسال إاقلد الولغن

اخلانق للالعد ويسال امعد ام اتر له معد تدإق اخل ق و

كاق الصالاد يس خدد لو ن معد ال دإق إإق الصالاد ى ء يلاره ليعاللل ا ملدر ملن إلروق الولغن أقلل إإ ا -: من إرق الوغن اخلانق للصالاد والذر ميكن حسانه لكل صالاد كالا يل

Choked pressure drop :

When the differential pressure across the valve increases the

flow rate will increase proportionately, but at a certain

differential pressure (pressure drop), any further increases in

the pressure drop will not increase the valve flow rate due to

the cavitation effect in liquids and sonic velocity in gases, this

pressure drop is called choked pressure drop and the flow rate

is called choking flow rate :-

If the flow rate is controlled by a valve, the valve must be

selected to operate in a range of press-ure drops less than the

choked pressure drop which can be calculated as follows :-


Friction Losses through valves:

Friction Losses through valves can be determined graphically from Figure 84. In an equivalent length of a pipe has the same diameter of the valve by applying the following procedure:-

1- Draw a line from the point of valve at the lift column to the point of the line inside diameter of the line pipe at the right column.

2- Read the value of intersection point at the equivalent length scale to determine the additional length to the case study line.

3- It is 1700 feet length of 24 in. line for gate valve 3/4 closed, 76 feet of 12 in. line for fully open swing check valve.


The equivalent length is added to the piping length in which the valve is mounted and the total friction losses shall be calculated for the whole length.

FIGURE 84: Resistance of valves to flow of fluids.


INDEX

(3)Valves Basic Parts : (Body, Bonnet, Disk and Seat, Stem, Actuator, Packing)

(9)Valves Classification: (9) By Mechanical Motion: (Linear, Rotary, Quarter Turn) (11)By Size: (Small, Large) (11)By Pressure, Temperature Rating:(Cold, NFPA, Steam Pressure, Multi Rating) (13)By Main Function: (13) Isolation: Isolating Valves. (14)Regulation: Regulators. (23)Non Returning : Check Valves. (36)Relieving: Relief Valves, Safety Valves. (49)Pilot-operated: Pilot-Operated Valves. (49)E-Signal-Operated: Solenoid or Pilot Valves. (53)By Closure Element Shape: (54)Gate Valves. (68)Globe Valves. (79)Ball Valves. (88)Plug Valves. (98)Diaphragm Valves. (104)Pinch Valves. (106)Butterfly Valves. (110)Needle Valves. (114)By Operating Method: (manual, Actuating). (115)Actuators: (115)Manual:(Simple, Hammer, Geared)Handwheel (117)Automatic: (118) Pneumatic Actuator. (124) Electro Mechanical Actuator. (130) Electro Hydraulic Actuator. (133)Actuator Selection. (136)Control System:(Control Signal, Electro Control). (142) Valve Tests of API 598


(156)Installation: (157)Pre installation Inspection. (158)Test Equipment. (160)Installation Criteria. (171)Commissioning. (175)Routine Maintenance: (178)Reconditioning Nozzles and Disks. (182)Replacing Actuator Diaphragm. (185)Replacing Seat Rings. (186)Grinding Of Valve seat. (187)Adjusting The Stem Connector. (191)Routine Maintenance Of Packing Box. (194)Spare Parts. (196)Trouble Shooting. (203)Valve Selction. (206)Engineering Of Flow Through Valves. (212)Index.

===================================

اللهم أنفعنا بما علمتنا و

العالمين رب هلل الحمد

جاريه لروح من أعده اللهم اجعل هذا العلم صدقة (213)

VALVES TRAINING PROGRAM Introduction: This program has been prepared by Eng. ALY FARAG who has a special web site http://alyfarag.jeeran.com/ about petroleum science and news.

ALY FARAG has a long experience (38years) in piping systems in which all different types of valves are used. Along his work he faced a lot of valve troubles which could be shot, so he has decided to prepare this program because the valves are generally considered critical components in any piping system.

Who should attend the program?

Engineers, supervisory and technical staff involved in operation and maintenance of piping systems.

Program Objectives: The program provides participants with knowledge needed to be effective in design, testing, installation, precommessioning, commissioning, routine maintenance, and trouble shooting. By this knowledge participant can easily select and specify the proper new valve and maintain the existing valves to avoid any internal and external leakage in the piping system.

Program duration: 5 days.

Program outline: Day 1 : * Valves Basic Parts. * Valves Classification. * Isolating Valves. * Regulating Valves. * Non Returning Valves. * Pressure, Temperature rating.

http://alyfarag.jeeran.com/

Day 2:

(Design, Advantages, Disadvantages, Applications)

* Gate Valves. * Globe Valves. * Ball valves. * Plug Valves.

Day 3:

(Design, Advantages, Disadvantages, Applications) * Diaphragm Valves. * Pinch Valves. * Butterfly Valves. * Needle Valves.

Day 4: Actuators

* Classification. * Manual Operated Actuators. * Automatic Operated Actuators. * Selection Of Proper Actuator.

* Control System.

Day 5:

* Valve Tests according to API 598 * Installation(precommissioning, Commissioning) * Routine Maintenance. * Trouble Shooting. * Valve Selection. * Flow Engineering Through Valves.

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