Chapter 4 Valves

Chapter 4

Valves

HYDRAULIC AND PNEUMATIC

Type of Valves

Power

Supply

Control

Output

DCV

FCV

PCV


Type of Valves

Basic DCV is A Check valve.

A Check Valve allows flow in

one direction.

The diagram show a basic inline

check valve.


Directional Control Valve : Check valve

Free-flow direction No-flow direction


Directional Control Valve : Check valve

Free-flow direction No-flow direction

In the free-flow direction, the fluid pressure

overcomes the spring forces.

The higher the pressure, the greater will be

the force pushing the poppet against it seat

If flow is attempted in the opposite direction,

the fluid pressure pushes the poppet (along

with the spring force) in the close position.


Check Valves in Circuit

Question :

A pressure relief valve has a 4.2 cm2 area of poppet on which the

system pressure acts. A spring which is initially compressed 0.5 cm

from its free length condition, has a constant of 3200N/cm is

holding the poppet against it seat. The full flow can be achieved

when the poppet is moved 0.3 cm from the initial fully closed

condition. Calculate the cracking pressure and full flow pressure of

the valve.


Bypassing using Check valve

A Check Valve can be used for

component bypass, since it give

the circuit line the lowest

resistance to the line.

Check valve = Injap sehala


Pilot check valve

Another type of Check Valve is

pilot to open check valve.

The pilot line refers to a line where

it received command from the fluid

itself.

It always permits free flow in one

direction but permits flow in the

normally blocked opposite direction

only if pilot pressure is applied at

the pilot pressure port of the valve.

Pilot to Open Check Valve = Injap

sehala buka kendalian pandu.

Pilot to close check valve will

block the free flow if the pilot

pressure is applied.


Pilot to Open Check Valve in Counterbalance Circuit.

What happened if the NORMAL check valve is used or without check valve?


Pilot to Open Check Valve in Counterbalance Circuit.


Shuttle Valve

Shuttle Valve allow two alternated flow to

be connected into the line.

In Short : 2/2 DCV, 2/2 Way Valve.

In Full : 2 Way, 2 “Spool” Position Valve.


DCV Valves : How to Classified?


Type of 2/2 Way Valve. (Normally Open and Normally Closed)

2/2 Way Valve (Normally Close) type 2/2 Way Valve (Normally Open) type


Type of 3/2 Way Valve. (Normally Open and Normally Closed)

3/2 Way Valve (Normally Open) type 3/2 Way Valve (Normally Closed) type


3/2 Valve (Normally Closed)

Use for single acting cylinder

NORMAL POSITION ACTUATED


3/2 Valve (Normally Closed )

NORMAL POSITION ACTUATED


4/2 Valve (PB Type )


4/2 Valve (Lever type ) NORMAL POSITION

Use for double acting cylinder


4/2 Valve (Lever type ) ACTUATED

The four way, two position DCV used in previous circuit are sometime impractical

since they continuously sending flow and pressure into hydraulic actuator. The should

give a relief to the actuator, a NEUTRAL position should be used, where the actuator is

not subjected to pump pressure.


NEUTRAL POSITION

4/2 Valve

4/3 Valve


4/3 Valve With Closed Neutral Position

Closed Neutral Position:

(1) The Pump is blocked.

(2) The flow goes to Pressure Relief

Valve.

(3) The maximum allowed pressure

of the system is set by the

pressure relief valve.


4/3 Valve With Tandem Neutral Position

Tandem Neutral Position:

(1) A desirable condition where the

only pressure involve line

resistance.

(2) The power consumption is

reduced. Is said to be

UNLOADED.

(3) Less energy wasted.


4/3 Valve With Float Neutral Position

Float Neutral Position:

(1) A desirable condition for a

circuit with motor, since it allow

the motor to spin until fully stop.

(2) This condition is said to allow

the motor to float or spin freely

without influence of pump.

(3) Not using it may caused

pressure increase at the motor,

since spinning motor might give

a resistance when the positioned

is changed.


4/3 Valve With Open Neutral Position

Open Neutral Position:

(1) A combination of a tandem and

float neutral position.

(2) A flow will return to the tank

from the pump.

(3) At the same time, A bit of flow

might still be flowing (floating)

at the actuator.


4/3 Valve With Regenerative Neutral Position

Regenerative Neutral Position:

(1) A term used where the flow

returning from actuator is feed

back into the pressure line to

give supplemental power.


Valve Actuated: Direct and Pilot

Hydraulic oil in Pilot Line only

help in changing the position of

the valve, it does not get mixed

with the oil that is flowing

inside the valve.

Push button 4/2 way directional

control valve with spring return

Pilot 3/2 way directional

control valve with spring return

• Actuation: To switch position.

• Return : To switch back to initial condition.

DCVs Actuation and Return


The way to actuate the Valves.

Lever


The way to the actuated valve RETURN to normal position.


Example of Directional Control Valve.

Flow Control Valves

Flow Control Valve

• Main purpose : to regulate speed.

• All FCVs control cylinder speed by

regulating the flow rate.

• Can be of:

– Fixed Orifice and Restrictor

– Adjustable Orifice and Adjustable Restrictor

– Pressure compensated and Non pressure

compensated valve.

– One-way flow control valve.

– Deceleration valve.

– Flow Dividers

– Proportional Flow control valves.

• Fixed orifice : provided fixed /

constant flow control which is

NOT influenced by the fluid

viscosity.

• Fixed restrictor : provided fixed

/ constant flow control which is

influenced by the fluid viscosity.

Fixed Orifice and Restrictor


FLOW CONTROL VALVE : Needle valve.

Basic FCV is a needle valve.

A needle valve control the flow

rate in the circuit.

By controlling the flow rate, the

speed of the actuator can be

controlled.

Controlling the flow rate is called metering the flow, in hydraulics.

• Variable orifice : provided flexible

flow control which is NOT


• Variable restrictor : provided

flexible flow control which is


Variable Orifice and Restrictor

(Needle Valve)

• Non-pressure compensated

FCV : useful when the load is

constant.

• Only suitable for a constant

system pressures

• If pressure changes, speed and

flow rate changes.

• Pressure compensated FCV :

useful for variable loading.

• Always maintain the flow rate

and the speed if pressure

changes.

Pressure and Non-pressure Compensated

FCV

A one way FCV is an integrated

needle valve with a check valve.

A one way FCV give a controlled

flow direction from left to right

(A) and a free flow in reverse (B)


FLOW CONTROL VALVE : One way FCV

The term “meter-in” or

“metering in” means that we

are controlling the flow that

goes INTO the cylinder.

The Figure show “meter-in”

flow control during extension

only.

The meter-in here is only for

extension of the cylinder.

Remember that that is no

metering / no flow control is

done on the retraction of the

cylinder.


“Meter-In” : Controlling the Flow into the Actuator (In case of extension only)

Remember that in this case, no


done on the extension of the

cylinder.

The Figure show “meter-in”

flow control during retraction

only.

The meter-in here is only for

retraction of the cylinder.


“Meter-In” : Controlling the Flow into the Actuator (In case of retraction only)


“Meter-Out” : Controlling the Flow out from the Actuator (In case of extension only)

The term “meter-out” or

“metering-out” means that we

are controlling the flow that

goes OUT FROM the cylinder.

The Figure show “meter-out”

flow control during extension

only.

The meter-out here is only for

extension of the cylinder.

Remember that that is no


done on the retraction of the

cylinder.


“Meter-Out” : Controlling the Flow out from the Actuator (In case of retraction only)

Remember that in this case, no


done on the extension of the

cylinder.

The Figure show “meter-out”

flow control during retraction

only.

The meter-out here is only for

retraction of the cylinder.


When to use Meter-In and Meter out ??

It usually depends on the load.

When we handle resistive load, we can use Meter In.

Resistive load is the load that resist the oil flow.

When we handle tractive load, we can use Meter Out.

Tractive load is the load that follow the oil flow.

Tractive Load Resistive Load


Consequence of Metering in and out.

There is no consequence of using

“meter in” flow control for resistive

load.

However, by using meter-out for

tractive load can cause pressure

intensification.

This pressure intensification is ok if it

within the operating pressure limit of

the actuator, if it is out of the operating

pressure limit, the actuator can be

damaged/break /leak.

REMEMBER!!!! The positioning of

metering in or out is also differ with the

position of the load, whether towards

upward, downwards or in horizontal

movement.

Pressure intensification.


Meter-in flow control for both stroke extend and retract.


Metering in for extension and metering out for retraction

Why metering out when we retract?

Cause the load act as a tractive load. As long

as the actuator can bear the pressure

intensification.

Why metering in when we extend

Cause the load act as a resistive load.


PRESSURE CONTROL VALVE

The most widely used of PCV is

Pressure Relief Valve.

A Pressure Relief Valve limit the

maximum pressure in hydraulic circuit by

giving alternate direction to the flow when

it reach certain pre-set pressure level.


Pressure Relief Valve : The Application in the Circuit

PCV

Normal position

Pressure control valve practically is

used in every hydraulic system.

It is normally a closed valve whose

function is to limit the pressure to a

specified maximum value by diverting

oil from pump flow back to the tank.

Refer to the circuit : When the motor is

on and the control valve is un-actuated,

the fluid pressure in the pipe line will

increase. At the maximum pressure, the

pressure relief valve will open and

allow the fluid to return back to the

tank Without the pressure relief valve

the pipe line may explode or the pump

damage.

If the valve is actuated, the piston will

extend. When the piston fully extend

the pressure will also increase and

again the pressure relief valve will

open.


PRESSURE CONTROL VALVE : Variation

Why do they

need external

drain?


PRESSURE REDUCING VALVE



These are used to provide a constant pressure to part of a system that is lower than the

pressure in the rest of the system.

The design is very similar to the two stage pressure relief valve but the motion of the

piston is controlled by the outlet pressure, not the system pressure.

The high pressure oil leaks through the restrictor and lifts the poppet. The pressure is

set by adjusting the spring behind the poppet.

The oil passing through is wasted to drain. The pressure drop through the restrictor

produces a force imbalance on the spool and it moves to partially block port B and so

reduce the pressure at port B.

If the pressure on port B rises, the leakage through the restrictor increases and the

pressure drop increases so the spool moves further close port B.

If the pressure on port B drops, the leakage drops and the pressure difference drops so

the spool moves to open port B and let more oil through.



Pneumatic systems are low pressure systems and are supplied with air at a typical

pressure of 8 bar and this is reduced to supply the system typically at 3 bar.

The air is supplied to the system through a regulator which is a form of reducing

valve.

The pressure is reduced through the poppet valve (2). The valve is set by the spring

and adjuster (4).

Variations in the outlet pressure make the diaphragm (3) move up or down to open

and close the valve as required to keep the pressure constant.


VALVE SYMBOLS


VALVE SYMBOLS

END OF CHAPTER 4

THANK YOU

Chapter 4 Valves

Documents

regenerative

pneumaticpressure

float neutral

pneumaticpressure

pneumaticflow

directional

tandem neutral

pneumatic