HYDRAULIC AND PNEUMATIC CONTROL ELEMENTS

NECESSITY OF FLOW CONTROL VALVES The control of fluid dynamics is essential to ensure

efficient, reliable and safe operation of pumping systems. A pump puts fluid in motion by adding energy to it.

This kinetic energy, observed as pressure, is carried in the fluid and slowly lost to friction in the piping system.

Uncontrolled fluid in motion can physically destroy the pump, piping, valves, meters and other system components. 

FLUID CONTROL VALVESPressure Control Valves

Flow Control Valves

Direction Control Valves

1. Pressure Relief- Directly operated- Pilot operated

2. Counter balance

3. Pressure reducing

4. Sequencing valves

1. Non compensatedFlow Control valve

2. Pressure compensated

flow Control valve

3.Temp. compensated flow Control valve

1. 2/2, 3/2, 4/3 valves

2. Manually operated

3.Solenoid operated

4. Pilot operated

5. Cartridge valves

6. Check Valves- Directly operated - Pilot operated

Method of actuation1. Directly operated2. Pilot operated3. Manually operated4. Electrically operated

PRESSURE CONTROL VALVES

1.Pressure Relief Valve

- Directly operated- Pilot operated

2. Pressure Control Valve

3. Sequence Valve

1. PRESSURE RELIEF VALVE-This valve used to limits the pressure in the whole system.

-Also called as Safety valve or Maximum Pressure valve.

-Pressure relief valve is normally closed type valve.

-It is located between the Pump and direction control valve (Before the actuator)

Directly operated

Pilot operated

PRESSURE REDUCING VALVE

Directly operated

- Pressure reducing valve is used to maintain pressure in second branch of the system.

Main BranchP1

Second BranchP2

SEQUENCE VALVE The sequence valve is used to supply the flow of fluid to second

consumer if requirement of first consumer is fulfilled. It consist of pilot relief valve. Also consist of two spools connected to each other.

COUNTER BALANCE VALVE This valve is used to avoid uncontrolled movement of cylinder. This valve is used in earth moving equipments. It consist of two pilot relief valves are connected to each others. It holds the load for some time like lifting trolley of the tractors

or the trucks.

Fluid is controlled by resisting it from one side and free from its other side.

FLOW CONTROL VALVE Flow control valve is used to control the flow rate in the system

according to system designed.

Flow rate is controlled by the throttling or the diverting.

Throttling means by using the orifices, throttle valves etc. and diverting means bypassing it to reservoir using the flow control valve.

NON-COMPENSATED FLOW CONTROL VALVE In such valves Pressure, velocity and flow rate will get varies. It

will not remain constant. The orifices, throttle valve are come in this above valve.

Pressure Compensated Flow control Valve

Pressure - Temperature Compensated Flow control Valve

Variable Flow control Valve

Non return type Flow control Valve

CHECK VALVE OR NON-RETURN VALVE This valve allows the flow of fluid in only one direction bur dose

not allow flow in other direction. Also called as Non Return valve.

Directly operated check valve (Poppet type)

Pilot operated check valve (Poppet type)

Shuttle valve

Quick Exhaust Valve

DIRECTION CONTROL VALVE The Direction Control Valves are used to change the

direction of flowing fluid. We have required to move the actuator in the

different direction and it is actuated by supplying the fluid in different directions using D.C.V. 2/2

DCVPorts Positions

METHOD OF ACTUATIONS FOR D.C.V.

2/2 DIRECTION CONTROL VALVE

•This is the 2/2 DCV which is spring operated type.

•Here both OFF and ON positions of the valve are shown in the above figures.

•If fluid is coming from pump, the spring moves towards right and port P is connected to port A and fluid is supplied to actuator.

3/2 DIRECTION CONTROL VALVE

P

A

R R

A

P3/2 DCV symbol

4/2 DIRECTION CONTROL VALVE (SPOOL TYPE)

P

A

R R

A

P

B B

4/2 DCV symbol

4/3 DIRECTION CONTROL VALVE 4/3 DCV having the 4 ports and 3 position for the

actuation of it. In three positions this valve will be actuated. The symbol of this particular (4/3 DCV) valve is given

below.

According to center positions of above valve it is classified in three types.

1. Closed Center position valve2. Open Center position valve 3. Tandem Center position valve

P

A

R R

A

P

B B

4/3 DCV symbol

A B

P R

1. Closed Center position valve

2. Open Center position valve

3. Tandem Center position valve

• In this position all the ports are closed to each other.• Possibility of Heating and Damage

• In this position all the ports are open to each other.• No Possibility of Heating and Damage.• No work is done by any component.

• Used to holds the work load for some time period.• No heating and damaging. Also supply the fluid to other circuit so, extra power •station is required.

SEAT TYPE DCV (4/2 TYPE)