01 General Control Valves Training

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Transcript of 01 General Control Valves Training

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Engineering Centre of ExcellenceECoE - Doha, Qatar

Instrument training 16th July 2011General Control valves.

Prepared by: Gavhane D.V.

General Control valves.2

General Control Valves.

BY:-DNYANESHWAR GAVHANE Prepared by: Gavhane D.V.

General Control valves.3

General Control Valves. INTRODUCTION :-

Control valves also called final control element are a most important element in the control system of a process plant. It is the last device in control loop. DEFINITION :-

A control valve is a variable orifice used to regulate the flow of a process fluid in accordance with requirement of process.

FUNCTION :-

It absorbs the proper amount of pressure drop to maintain system balance under all operating conditions.

Prepared by: Gavhane D.V.

4

General Control Valves.Features of Control valves. THERE ARE FOUR FEATURES OF CONTROL VALVES :

CapacityRangeability CharacteristicsPressure dropCAPACITY : The capacity is normally measured as Cv (Flow Coefficient) which is defined as :

The number of US gallons per minute of water at 60oF that will flow through a valves with 1psi pressure drop .

RANGEABILITY : Rangeability of a Control Valve is the ratio of the maximum to the minimum controllable flow. Prepared by: Gavhane D.V.

5General Control Valves.Control valves and Flow Characteristics. The relationship between control valve capacity and valve stem travel is known as the Flow Characteristic of the control valve.

The Curve shown are based on constant Pressure drop across the valve and called Inherent flow characteristics. Prepared by: Gavhane D.V.

6General Control Valves.Linear Characteristics. Flow Capacity increases linearly with valve (stem) travel. In which the valve differential pressure drop is Constant over the travel range.Linear valve plug shall for liquid level control and control application requiring constant gain.

LINEAR VALVE TRAVEL IS DIRECTLY PROPORTIONAL TO THE VALVE STROKE

FOR SLOW FLUID TRANSFER PROCESSMORE THAN 40%OF SYTEM PRESSUREDROP ACROSS VALVEPrepared by: Gavhane D.V.

7General Control Valves.Equal Percentage Characteristics. Flow Capacity increases exponentially with valve trim travel .Equal increment of valve travel produce equal percentage change in existing Cv.Equal Percentage valve plug shall be used where only small percentage of system drop is available in Control valve. EQUAL INCREMENT OF VALVE TRAVEL PRODUCE AN EQUAL PERCENT FLOW CHANGE

FOR FAST FLIUD TRANSFER PROCESSHIGH RANGEABILITYPrepared by: Gavhane D.V.

8General Control Valves.Quick Opening Characteristics. Provides large changes in flow for very small changes in lift or in which a maximum Cv is achieved with minimal closure member travel. It has too high valve gain.

LARGE INCREASE IN FLOW WITH A SMALL CHANGE IN VALVE STROKE

Quick opening valve are usually specified for ON-OFF Service such as sequential operation in either batch or semi continuous process and in self actuated control valve . When maximum valve capacity must be obtain quickly.

Cage- A part of a valve that surrounds the closure member & can provide Quick opening flow characterization.Prepared by: Gavhane D.V.

9General Control Valves.Cavitation. Cavitation is condition that occurs in liquid flow where the internal pressure of liquid at set point falls below vapour pressure and vapour bubbles form and at downstream rises above vapour pressure again.As this pressure recovers so that bubbles collapse and cavitation take place.It is possible to predict where cavitation will occur by looking pressure condition and valve recovery factor.( sigma Method )Cavitation sounds like stone passing through the valve.

Bubble formBubble collapseVena ContractaPP

PvPRESSURE PROFILE ACROSS SINGLE SEATED CONTROL VALVEPrepared by: Gavhane D.V.

10General Control Valves.Effect of Cavitation.

Erosion in rotary plug valve body induced by cavitationPrepared by: Gavhane D.V.

11General Control Valves. Flashing.Flashing is condition that occurs with liquid flow where the Pressure fails below it . There are then two phases flowing ( i.e. Liquid and vapour ) down stream.Several damage can occur inside a valve due to erosion caused by the impact of liquid droplet traveling at high speed.

Bubble form

Vena ContractaBubble continue down streamP1Pv

P2PRESSURE PROFILE ACROSS SINGLE SEATED CONTROL VALVEPrepared by: Gavhane D.V.

12General Control Valves.Effect of Flashing.

Typical trim erosion damage due to flashingPrepared by: Gavhane D.V.

13General Control Valves.Velocity Profile across Single seated Valve.

P1P2 V 1(Liquid)V 2 (Liquid)PRESSURE PROFILE ACROSS SINGLE SEATED CONTROL VALVEPressure Recovery:- At vena contracta,the velocity is greatest & substantially decrease in pressure .Further down stream, as the fluid stream expands into a large area, Velocity decreases and pressure increases. This phenomena is called Pressure recovery.As a general ,globe valves have Lower pressure recovery than Ball and Butterfly Valves.

PvPrepared by: Gavhane D.V.

14General Control Valves.Piping Influence/Reynolds Number/Choked Flow. Piping Influenence:- Capacity reduction due to the presence of Reducer Up & Down stream of the valve. Correction factor will be available from manufacturer .Reynolds Number :- For Reynolds number application such as viscous or small flow , the basic sizing equation can not be used without correction, since the equation is based on turbulence flow . Correction factor will be available from manufacturer .(The ratio of dynamic forces to viscous forces) Usually the correction can be ignored when Reynolds number is greater than 4000,the correction will be 10% or less .Choked Flow:- When the pressure at vena contracta drop below the vapor pressure of the liquids, bubbles will form in the stream .The formation of bubbles causes a crowding condition at vena contracta which tends to restrict flow, and further increase in pressure drop will not produce increase in flow. In case of gas , choked flow means outlet velocity reaches sonic velocity.The limiting Pressure difference Pt is called Maximum allowable differential pressure for sizing.

Prepared by: Gavhane D.V.

15General Control Valves.Contents of Control Valve: Data Sheet PROJECT:-GPS DOC NO:--CONTRACT NO:-SUB CONTRACTOR DOC NO:-SHEET NO:-1 OF 1DOCUMENT NAME:-SPECIFICATION AND DATASHEETS FOR CONTROL VALVESCLIENT DOC NO:-DATE:-REV NO:-DATASHEET - CONTROL VALVES1GENERAL DATA TAG2 SERVICE BLANKET FUEL GAS FROM OIL STORAGE TANK 0-T-36033 LINE NO. / PID NO. 0-14"-FG-43 0017-AA3-H(E) / S2-01-YS207019-PID-P-5004 Sht 1 of 24 FLUID TANK VENT/FUEL GAS CRITICAL PRESS. Pc5SERVICE CONDITIONUNITMAX FLOWNORM FLOWMIN FLOW SHUT-OFF 6 FLOW RATEm3/h51661847525.3-7 INLET PRESSUREpsi(g)0.05680.0930.097515 bar(g)8 OUTLET PRESSUREpsi(g)0.0370.00870.002349 INLET TEMPERATUREDegree C505050100(Note 1)10 SPEC WT/DENSITY/ MOL WT- /kg/m3 / kg/kmole/-/1.378/40.30/-/1.378 /40.30/-/ 1.381/40.30-11 VISCOSITY /SPEC HEAT RATIOCp / 0.00924/1.1330.00924/1.1330.00924/1.133-12 VAPOR PRESSUREinH2ONANANA-13 REQUIRED CV-14 TRAVEL%015 ALLOWABLE /PREDICTED SPLdBA< 85/< 85/< 85/-16 SET POINTinH2O(g)2.752.752.75

Prepared by: Gavhane D.V.

16General Control Valves.Contents of Control Valve: Data Sheet. 17LINE PIPE LINE SIZE & SCHEDULEIN14" & SCH20 56ACTUATOR (PNEUMATIC) TYPE SINGLE-ACTING FAIL SAFE SPRING RETURN DIAPHRAGM TYPE18OUT14" & SCH20 57 MFR & MODELVTS19 PIPE LINE INSULATIONHEAT CONSERVATION (ELECTRICAL TRACING)58 SIZE / EFF.AREAVTS20SPEC.& CODES VALVE SIZINGISA S75.0159 ON/OFFMODULATINGYES21 VALVE SEAT LEAKAGE CLASSIV AS PER FCI 70-260 SPRING ACTION ON FAILCLOSE2261 MAX ALLOWABLE PRESS.VTS2362 MIN REQUIRED PRESS.VTS2463 AVAILABLE AIR SUPPLY PRESSURE kPagMINNORMAXDESIGN25VALVE BODY TYPEBUTTERFLY64400850900100026 SIZE VTS65 BENCH RANGEVTS27 MAX PRESS./TEMP.VTS66 ACTUATOR ORIENTATIONVTS28 BODY/BONNET MATERIALA105 or A216 WCB67 HANDWHEEL TYPEYESVTS29 LINER MATERIAL / ID68 AIR FAILURE LOCK RELAYREQD.SET ATNote 53069 AIR BOTTLEREQD. WITH ACCESSORIES31 END CONNECTION IN/ OUTFLANGED70 FIRE SAFEYES32 RATING & FLANGE FACE FINI.150# RF ASME B16.571POSITIONER INPUT SIGNAL4-20 mA33 END EXTENSION/MATERIALASTM A105 carbon steel72 TYPEELECTRO-PNEUMATIC (HART)34 FLOW DIRECTION YES73 EXPLOSION PROTECTIONEExd35 TYPE OF BONNETBOLTED74 ON INCR SIGNAL OUTPUT INCR/DECRFIELD REVERSIBLE36 LUB & ISO VALVE / LUBE75 GAUGESYesBYPASSYes37 PACKING MATERIALPTFE76 CAM CHARACTERISTIC38 PACKING TYPEVTS77 MFR & MODELVTS39 BONNET GASKETVTS78SWITCHES TYPE-QTY-40 MFR & MODELVTS79 MFR & MODEL-

Prepared by: Gavhane D.V.

17General Control Valves.Contents of Control Valve: Data Sheet . 41TRIM TYPE VTS80 CONTACTS/RATING-42 SIZERATED TRAVELVTSVTS81 ACTUATION POINTS-43 CHARACTERISTICVTS8244 BALANCED/UNBALANCEDVTS83AIR FILTER MATERIAL DIE CAST ALUMINIUM45 RATED CVVTSFLVTSXTVTS84 FILTER SIZE< or = 25 Micron46 PLUG/BALL/DISC MATERIALF685 SET PRESSURE47 SEAT MATERIALF6 SEAT HARD FACED WITH STELLITE6.86 INTEGRAL PRESS. GAUGE50mm DIAL48 CAGE/GUIDE MATERIALVTS87 CONNECTION1/2"NPT49 STEM MATERIALF688 MFR & MODELVTS508951SPECIALS / ACCESSORIES NEC CLASS GR. DIV.90TESTS HYDRO PRESS.YES52 IEC ZONE GR. TEMP. CLASSCLASS I, ZONE 2 , GROUP IIA & T391 SEAT LEAKAGE TESTYES5392 CAPACITY TESTYES54935594 NOTES :VTS-Vendor To Specify

Prepared by: Gavhane D.V.

18General Control Valves.Globe Control Valve Construction. .

Prepared by: Gavhane D.V.