Content : 4.1 Hydraulic and Pneumatic actuators. 10...

CH.4 Basic Components of Hydraulic and Pneumatic System/16 M HAP/17522/AE5G

R.K.Yadav/Automobile Engg Dept/New Polytechnic Kolhapur.

Content :___________________________________________________________

4.1 Hydraulic and Pneumatic actuators. 10 Marks

Hydraulic Actuators - Hydraulic cylinders (single, double acting andtelescopic) –construction and working, Hydraulic motors (gear and pistontype) – construction and working.

Pneumatic Actuators - Pneumatic cylinders (single and double acting) -construction and working, Air motors (gear and piston type) -construction and working

4.2 Valves for Hydraulic and Pneumatic systems. 08 Marks

Classifications of valves, poppet, ball, needle, throttle, pressure controldirectional control, sequencing synchronizing ,rotary spool, sliding spooltwo position, multi position. Non-return valves. Proportionate valve

Construction and operation of above valves.

4.1 Hydraulic and Pneumatic actuators.



Hydraulic actuators :

These are the elements of hydraulic system which transform hydraulic energy intouseful work, through these device we can achieve objectives like moving ,grippinglifting ,rotary motions with force.

Single acting cylinder with single piston rod :

This type of cylinder is used for comparatively lower loads than plunger or ram typehydraulic cylinder. This cylinder may be gravity return or spring return.

Its applications mostly in production tooling for clamping pushing etc also inautomation plant where number of cylinder perform individual operations in apredetermined sequence.



Rotary Actuators :

Rotary actuators are used to generate rotary motion by using force of hydraulic oilor compressed air so it is categories into two types Hydraulic motor and air motor.In which pressure energy converted into mechanical energy.

Classification of hydraulic motors are as bellow,

1) Gear motor similar to Gear pump.2) Vane motor similar to vane pump.3) Swash plate piston motor.4) Bent axis piston motor.5) Radial piston motor.

Construction of hydraulic pump and motors are similar with each other onlydifference is that for operation of pump there is need of prime mover which aredirectly coupled with pump. In which mechanical energy is converted into pressureenergy.

Applications of hydraulic motor :

hydraulic motors are used for Industrial and Civil Engineering task for docks andmoving bridges, Crane drives, Military vehicles, Excavators, Conveyors and feederdrives, Plastic injection machine, Drill machine, Trench cutter etc.

Gear type hydraulic motor :

Gear type motor is a rotary actuator used to rotate the shaft. It consists of twogears in mesh with each other. One gear is connected to output shaft and other isidler. Both the gears are mounted in closed casing. Pressurized fluid enters from thebottom, and pressurizes the chamber. This pressure exerts a force on teeth, Theseforces results in rotation of both gears. This rotary motion is further used in rotation



of output shaft. Gear motors suffer from leakage, which is quiet high at low speeds.Hence gear motors are used where medium speed and low torque are required.



Vane type air motor :

A typical vane type air motor is shown in fig. These motors are simple inconstruction, extremely compact. The rotating element is a slotted rotor whichis mounted on a drive shaft. Each slot of the rotor is fitted with a freely slidingrectangular vane. The rotor and vanes are enclosed in the housing, the inner surfaceof which is offset from the drive shaft axis. The compressed air is made to passthrough inlet ports and this air flows over the vanes and is exhausted through theoutlet, causing the shaft to rotate. The speed of air motor can be varied by varyingthe air flow to the motor.



OR

Construction and Working of Piston type air motor :

Radial Piston Motor :

In this, three pistons are fitted in cylinder block. The curve ends of pistons canrest on smooth surface of rotor. Cylinder block and rotor are rotating member ofmotor.If compressed air is introduced in the cylinder under pressure, piston will pushedoutward in its cylinder. This principle is used in this motor. Suppose compressed airunder pressure is admitted to cylinder no 1, piston will move outward in its cylinder.Now curved end of piston will slide inside the rotor with force and rotor will turn inclockwise direction. Then the cylinder no 3 will occupy the position of 1 sincecylinder block also starts rotating. And same cycle will start which results inrotational motion of rotor. These motors produce high power and torque.



2) Axial Pistonmotor :

Constructionand Working :

In axial piston motors, the piston reciprocates parallel to the axis of the cylinderblock. These motors are available with both fixed-and variable-displacementfeature types. They generate torque by pressure acting on the ends of pistons



reciprocating inside a cylinder block. The figure illustrates the inline design inwhich the motor, drive shaft and cylinder block are centered on the same axis.Pressure acting on the ends of the piston generates a force against an angledswash plate. This causes the cylinder block to rotate with a torque that isproportional to the area of the pistons. The torque is also a function of theswash-plate angle. The inline piston motor is designed either as a fixed- or avariable-displacement unit. The swash plate determines the volumetricdisplacement.

4.2 Valves for Hydraulic and Pneumatic systems.



Function of valve : (any four)

1. Blocking or stopping of flow.2. To release the flow of working medium.3. To give the Direction of flow.4. To maintain the Pressure of working medium for safety purpose.5. To maintain Flow quantity as per requirement.

Poppet valve :-

It consists of simple disc, cones or balls are used in conjunction with simple valveseats to control flow. When a push button is depressed, it lifts ball to its seat andallow fluid to flow from port ‘P’ to port ‘A’. When button is released, spring & fluidpressure forces the ball up again closing the valve. A poppet valve quickly opensrelatively larger orifice in a shorter travel to permit full flow of air thus it is fastresponse time. These valves are simple, cheap and insensitive to dirt.

Spool Valve : 1. Sliding spool :



It consist of a spool which moves axially within the valve body to control thedirection of flow. The body has inlet & outlet port. The inlet port is connected topump & outlet to actuators. The spool is moved by actuating mechanism or pushbutton. Normally valve is in closed condition. When push button is pressed the spoolmoves to left side & land on the port P. so that the valve is in open position. Whenthe push button is released spring forces spool to return to closed condition.

Sliding spool type Direction control valves are the following types- 2/2, 3/2 and 4/2.

2. Rotary spool Valve :

A rotary spool valve has a rotary spool which has internal oil passages to carry outthe direction control element. As shown in the figure the valve body has fourpassages pressure (P), return(R) and two connections to load (A & B). Figure showsthe three positions of the spool and respective port connections. As compared tosliding spool the rotary spool valve is less motion to operate, but it may need moreoperative force to switch the position.

OR

Rotary spool Valve :



It consist of a rotating spool which aligns with a hole in the valve casing to giverequired operation. Openings in casing are connected to compressor, and two sidesof cylinder i.e. port A and port B. When rotary spool is rotated the compressor portis connected to cylinder port A causing pressurized air to move the piston at thesame time port B is open to atmosphere. When spool returns to original positionpressure port and cylinder port is blocked and valve is in neutral position. Rotaryvalves are compact, simple & have low operating forces. They are low pressuredevices & hence used for hand operation in pneumatic systems. Leakage control israther difficult as rotary valves require close contact between port plate and spool.Leakage is important in high pressure. Hence they are better suited for low pressureapplications.

Direction control valve (DCV) :

Direction control valves are used for direction the pressurized fluid to obtain differentpositions.

3 X 2 DC valve :


R.K.Yadav/Automobile Engg Dept/New Polytechnic Kolhapur. Page 20




3 X 2 DC valve :






3 X 2 DC valve :



Construction :

3 X 2 means 3 ports & 2 positions. In 3x2 DC spool type valve, spoolreciprocates in a finely finished bore. The spring is attached to front spool.

Working :

Position 1:(Actuated position)Figure shown is actuated position. Push button is pressed in the port P isconnected to port A and no flow through R. When spool is pressed in spring iscompressed.

Position 2 (Normal Position)Now push button is released, spring will expand and spool will move towardsright. Now port A will be connected to port R and Port P will be disconnectedso that flow of used oil will start from port A to R and then to oil reservoir.

4/2 DC valve :

Construction :

It consists of a shaft sliding in a bore which has large groove around thecircumference. The spool is sealed along the clearance between moving spool andvalve body. The grooves guide the fluid flow by interconnecting or blocking theports. Spring is fitted in bore to bring the spool back to original position.A four-way has four ports labeled P, T, A and B.

P is the pressure inlet port. T is the tank; A and B are outlet ports to the system.



Working of 4/2 DC valve:

It has two switching positions.In the normal position, pump flow is sent to outlet B. Outlet A isconnected to the tank. In the actuated position, the pump flow is sentto port A. Port B connected to tank T.As soon as actuating force is released from spool, compression force of springbrings the spool back to original position.

4 / 3 DC valve : Symbol

Actuated position (Pulling action)



Normal position

Actuated position (Pushing action)

Construction:

Here 4/3 D.C. valve is shown in the fig. There are four ports, A and B are consumerports(ports going to actuator). P is pressure port through which pressurized oil goesin. R is return port through which used oil is return to oil reservoir. Valve is pushbutton operated ( manually ) valve regains by spring expansion. There are totalthree positions which are represented by three square block. Out of which centralone is closed position and other two are actuated positions.

Working :

When we have shifted the spool manually in such a manner that all ports are closeto each other. No flow from port P to A or B and no flow from port A and B to R.When D.C. valve attains this position, pressurized oil returns to reservoir via pressurerelief valve. While closed centre position is in active mode then flow will not takesplace. When sliding spool moves towards right side then pressure port P connectedto consumer port B and consumer port A connected to return port R. Similarly whensliding spool moves in a left hand side manually then pressure port P connected toconsumer port A and consumer port B connected to return port R.



Normal position


Construction:


Working :




Normal position


Construction:


Working :




Non return valve is also called as Check valve or one way valve.

Construction :

This valve consists of valve body with inlet and outlet ports having valve element likecone, ball or spherical poppet. The valve element is in corporate with speciallydesigned spring.

Working :

When pressurized oil comes in through port A it will lift up the cone by overcomingspring force and flow will start from port A to port B .When flow from A stops springwill expand and cone will block the flow hence only one direction of flow is possible.

Flow Control valve : (FCV)

It is used to regulate flow of pressurized fluid by which we can easily control thespeed of actuators.It is normally placed between direction control valve and hydraulic or pneumaticactuators.Flow control is by following method :

i) Throttling – It is nothing but passing of pressurized fluid through fixedrestricted path, like through Orifice

ii) Diversion – By diverting or bypassing part of pressurized fluid so thatactuator receives only portion perform its task.

iii) Flow divide -



Non-compensated flow control valves :

The non-compensated flow control valves create an orifice in a pipe to restrict theflow. The control element of the valve may be needle, globe type as in figure. Thenon-pressure compensated type is used where the system pressure are relativelyconstant and motoring speeds are not too critical. It works on the principle that theflow through an orifice will be constant if the pressure drop remains constant.Without compensation, flow through these simple valves can very at a fixed settingwith changes in pressure or temperature.

Fig. shows a non-pressure compensated flow control valve with its symbol. Itconsists of a check valve, which permits free flow in the direction opposite to theflow control direction. If the load on the actuator changes, then the system pressurewill change appreciably and also the flow rate through a non-pressure compensatedvalve will change for the same flow rate setting.

OR



Pressure compensated flow control valves :



Ball Valve :

Construction:

Ball valves control Flow & Pressure of the fluid inside the Hydraulic systems whichregulates & controlled linear & rotational movements of the applications. Rotary ballvalve are very similar to rotary spool valves but with more limited portingconfigurations. Although these are sliding element valve their good sealing isobtained by the use of seals which is shown in fig .They may be categorized as fullor reduced passage depending on size of the hole through the ball relative to thevalve ports. Ball valves are available in Steel, Stainless Steel, and Brass Materials.Ball valves can be made in Cast body / Forged body & also in Solid bar stock body.

Pressure control valve : (PCV)

It maintain desired pressure level in the various parts of hydraulic circuit.

Function :1) Set a pressure limit to protect the system.2) Regulating the pressure in certain portion in the system.3) Unloading the system pressure.4) Pressure related functions are performed.



Directly operated pressure relief valve :

Function :

It's function is to limit the pressure in the system & thus protect the individualcomponent and lines from high pressure and danger of bursting. If the pressure inthe system increased above a pre-set level, these valve open to release the fluid outof the system, so that the system pressure comes to normal.



Sequence valve :

Whenever more than one operations will perform in a sequential order then forproviding the flow to second operation when pressure level at a particular operationhas reached. It is used for sequencing operations one after another.

Construction and Working :

Sequence valve is nothing but pilot operated relief valve. It has a special spoolhaving specially drilled oil passage with internal orifice drain is directed to maindrain. In normal position sequence valve is closed when the operation of consumer 1is completed pressure starts building and when reaches set value of pilot relief valvefluid flows through spool to drain/ tank.

As the fluid flows through spool the orifice causes pressure difference betweenspring side and spool side. This pressure difference results in differential force whichlifts the spool causing it to uncover the port’ A’ thus supplying fluid to anotherconsumer ‘A’.



Sequence valve :







Sequence valve :







Question Bank

4.1 Hydraulic and Pneumatic actuators :

1) Give classification of hydraulic actuator.2) State the types of hydraulic actuators. Describe construction and working ofsingle acting cylinder with neat sketch.

3) Explain with neat sketch gear type hydraulic motor.

4) Explain working of gear type hydraulic motor with neat sketch.

5) Explain construction and working of piston type air motor with neat sketch.6) Explain with neat sketch vane type air motor.

4.2 Valves for Hydraulic and Pneumatic systems.

7) Write classification of control valves.

8) Give the classification of valves used in hydraulic systems. Write four functions ofvalve. 6 m

9) Which are the various valves used in Direction Controlling the air in pneumaticcircuit? Explain construction and working of any one valve.

10) Explain the function of relief valve in hydraulic circuit and sketch the same one.

11) Explain the construction and working of non-compensated flow control valve.

12) Explain constructions of ball valve with neat sketch.

13) Draw a neat sketch of non return valve and explain it.

14) Explain rotary spool valve with neat sketch.

15) What are the direction control valves? Explain construction of 3/2 directioncontrol valve.

16) Explain construction and working of sliding spool type 4/3 direction controlvalve.

17) Draw a labeled sketch of sequence valve and describe it’s working.

18) Write construction and working of non-return valve with neat sketch.

6m

19) Explain construction and working of 4/2 DC valve which is used in hydraulicsystems.

Content : 4.1 Hydraulic and Pneumatic actuators. 10...

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