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Chapter 4
Valves
HYDRAULIC AND PNEUMATIC
Type of Valves
Power
Supply
Control
Output
DCV
FCV
PCV
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
Directional Control Valve : Check valve
Free-flow direction No-flow direction
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
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
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
Pilot to Open Check Valve in Counterbalance Circuit.
What happened if the NORMAL check valve is used or without check valve?
HYDRAULIC AND PNEUMATIC
Pilot to Open Check Valve in Counterbalance Circuit.
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
DCV Valves : How to Classified?
HYDRAULIC AND PNEUMATIC
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
HYDRAULIC AND PNEUMATIC
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
HYDRAULIC AND PNEUMATIC
3/2 Valve (Normally Closed)
Use for single acting cylinder
NORMAL POSITION ACTUATED
HYDRAULIC AND PNEUMATIC
3/2 Valve (Normally Closed )
NORMAL POSITION ACTUATED
HYDRAULIC AND PNEUMATIC
4/2 Valve (PB Type )
HYDRAULIC AND PNEUMATIC
4/2 Valve (Lever type ) NORMAL POSITION
Use for double acting cylinder
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
NEUTRAL POSITION
4/2 Valve
4/3 Valve
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
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
HYDRAULIC AND PNEUMATIC
The way to actuate the Valves.
Lever
HYDRAULIC AND PNEUMATIC
The way to the actuated valve RETURN to normal position.
HYDRAULIC AND PNEUMATIC
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
HYDRAULIC AND PNEUMATIC
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
influenced by the fluid viscosity.
• Variable restrictor : provided
flexible flow control which is
influenced by the fluid viscosity.
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)
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
“Meter-In” : Controlling the Flow into the Actuator (In case of extension only)
Remember that in this case, no
metering / no flow control is
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.
HYDRAULIC AND PNEUMATIC
“Meter-In” : Controlling the Flow into the Actuator (In case of retraction only)
HYDRAULIC AND PNEUMATIC
“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
metering / no flow control is
done on the retraction of the
cylinder.
HYDRAULIC AND PNEUMATIC
“Meter-Out” : Controlling the Flow out from the Actuator (In case of retraction only)
Remember that in this case, no
metering / no flow control is
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.
HYDRAULIC AND PNEUMATIC
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
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
Meter-in flow control for both stroke extend and retract.
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
PRESSURE CONTROL VALVE : Variation
Why do they
need external
drain?
HYDRAULIC AND PNEUMATIC
PRESSURE REDUCING VALVE
HYDRAULIC AND PNEUMATIC
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.
HYDRAULIC AND PNEUMATIC
PRESSURE REDUCING VALVE
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.
HYDRAULIC AND PNEUMATIC
VALVE SYMBOLS
HYDRAULIC AND PNEUMATIC
VALVE SYMBOLS
END OF CHAPTER 4
THANK YOU