Week 3 1_hydraulics_valve3

 Pressure control valves (PCVs)
 Directional control valves (DCVs; direct- and
pilot-operated)
 Flow control valves (FCVs)
 Check valves

 To control and regulate pressure in hydraulic
system
 Types
◦ Pressure relief valve
◦ Pressure regulator

 connected with high-pressure and return low
pressure lines.
 used to limit the maximum operating
pressure in the high-pressure lines. The relief
valve consists mainly of a poppet, loaded by a
spring.
P
T

 The poppet is pushed by the spring to rest
against its seat in the valve housing. The spring
pre-compression force is adjusted by a spring
seat screw or by inserting distance rings.
 The following formula is used to calculate the
cracking pressure for this valve

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.

 Reduce the output pressure to safe/usable pressure.
 Automatically shuts off hydraulic flow at a certain
pressure.
A
P T

 DCVs are used to start, stop, or change the
direction of fluid flow.
 The valves are specified by the number of
connected lines (ways) and the number of
control positions.
 The control positions determine the way in
which the lines are interconnected, and
consequently the directions of fluid flow.

 E.g.
 A 4/3 directional control valve is connected to
the pressure line (P), return line (T), and cylinder
lines (A and B). In its neutral position, the valve
closes all of the four lines and the cylinder is
stopped. By switching the valve to any of the
other positions, the cylinder moves in the
corresponding direction.

 Types:
1. 2 ports/2 way
2. 3 ports/2 way
3. 4 ports/2 way
4. 4 ports/3 way

◦ 1 working port and 1 pressure port
◦ Control delivery by closing or opening the
passage

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

◦ 1 working port,1 pressure port and 1 tank connection
◦ Control delivery
 Normal position – P is closed and A to T is open
 Actuated position – T is closed, flow from P to A

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

◦ 2 working port (A, B), 1 pressure port and 1 tank
connection
◦ Control delivery
 Normal position – flow from P to B and A to T
 Actuated position – flow from P to A and B to T

4/2 Valve (Lever type) NORMAL POSITION
Use for double acting cylinder

4/2 Valve (Lever type ) ACTUATED

The 4/2 way 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

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.

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 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 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 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.

 Also known as non-return valve
 generally used to allow for free flow in one
direction
 prevent (obstruct) the fluid flow in the
opposite direction
 Type:
◦ Spring loaded
◦ Without spring

 FCV is used to regulate speed
 It limit the amount of flow in a main or
branch hydraulic circuit
 Types:
◦ Throttle valve
◦ One-way FCV

 Used to restrict the flow from
either direction
 AKA as needle valve.
 A throttle valve control the
flow rate in the circuit.
 By controlling the flow rate,
the speed of the actuator can
be controlled.
FCV: Throttle valve

 Restrict the flow in one direction while allowing a
bypass in the opposite direction
 Used to reduce the speed of cylinder movement
100%

 A one way FCV give a controlled flow direction
from left to right (A) and a free flow in reverse
(B)

Week 3 1_hydraulics_valve3

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Week 3 1_hydraulics_valve3