Chapter 7 Flow Control Valves and Other
Hydraulic Valves
Objectives:
The purpose of this chapter is to describe:
1. Operation of flow control valves, cartridge valve,
proportional valve and servo valve.
2. Throttle valves, combined flow control and check valves,
flow regulating valve , flow divider, cartridge valve,
proportional valve and servo valve.
3. Applications of flow control valves, cartridge valve,
proportional valve and servo valve.
Upon completing this chapter, you should be able to:
Explain the operation of the various types of control valves.
Identify the graphical symbols used for flow control valves.
Master the characteristics of cartridge valve, proportional
valve and servo valve.
7.1 Throttle valves
1 Characteristics of throttle orifice
q  C AT (  p )
m
( 0 .5  m  1 )
Δq2
Δq1
q
p
Conclusion:
Thin-wall orifices should be used for throttle orifices
7.1 Throttle valves
2 structure
Figure 7.2 throttle valve
with axial vee notch orifice
1.top cover 2.guide sleeve
3. valve body
4.spool
5.spring 6.bottom cove
Figure 7.3 throttle valve with a
spiral curve and thin bladed notch
1.hand wheel 2.spool
3. valve pocket 4. valve body
7. 2 combined flow control and check valves
p
4
p
1
p
5
6
7
3
2
1
2
2
p
1
Figure 7.4 flow control and check valve
1.top cover 2.guide sleeve 3. upper spool 4.lower spool
5 valve body 6. return spring 7. base plate
7.3 Flow regulating valve
1 Problem
The pressure drop variation of a throttle valve has great
influence on its flow stability.
How to remove the influence?
The solution is to add a correction loop.
2 Measure methods of some physical parameters
A
p
A A
p1
p2
A
p1
p2
pA  k ( x 0  x )
( p1  p 2 ) A  k ( x 0  x )
( p1  p 2 ) A  k ( x 0  x )
(1) pressure measure (b) pressure sum measure (c) pressure difference measure
7.3 Flow regulating valve
3 construction of a flow regulating valve
The valve consists of a pressure reducing valve and a throttle valve
in series, where the former maintains a constant pressure difference.
7.3 Flow regulating valve
A signal in the reducing valve is taken from the middlestream side,
just ahead of the throttle orifice.
Another signal is taken from downstream, just after the throttle
orifice
7.3 Flow regulating valve
4 flow path
p
px
T
p1 (  )   
 p2 ( )   
 p3 ( )
 p x  p ressu re d rop of th e p ressu rere d u cin g v alve
 pT  p ressu re d rop of th e th rottle valve
5 measure and control quantity
The pressure drop of the throttle valve  pT
7.3 Flow regulating valve
6 static equation
Equilibrium equation ΣF=K(x0+x)+p3A –p2A=0
That is
p2–p3=K(x0+x)/A
if the K is very small and x0>>x, p2–p3 ≈Kx0/A(constant)
Throttle equation q1=CAT(p2–p3 ) m
Thus
q1 ≈ CAT(Kx0/A ) m = constant
7.3 Flow regulating valve
7 Transient regulation
p1≈constant
p2= p1-Δpx
 L oad   p 3   x    p x   p 2   ( p 2  p 3） C 

  q 1  con st
 L oad   p 3   x    p x   p 2   ( p 2  p 3） C 
8 Application
The valve is usually used to adjust or stabilize velocity.
7.3 Flow regulating valve
Temperature compensation with an adjustable orifice
The spool is made of material with high thermal expansion
coefficient.
when the temperature increases, the spool is expanded so that
orifice is smaller, that will reduce the viscosity effect on the flow.
7.4 Flow divider
Flow dividers maintain equal flow rates in the branch
circuits even if the pressures in the branches are not equal.
Figure 7.8 symbol for flow dividers
(a) flow dividers
(b) flow combiners
(c) flow dividers & combiners
7.4.1 flow divider
sm all vent
sm all vent
figure 7.9 the operation principle of the flow dividers
1,2 – fixed orifices 3,4- the adjustable orifices 5- valve body
6- reducing pressure valve 7- spring
7.4.1 flow divider
q0 p0
sm all vent
p1
p2
p1
A
p
p2
q1 p3
q2 p4
sm all vent
q 1  C A1 ( p 0  p 1 )
m
q 2  C A2 ( p 0  p 2 )
Throttle equation:
Balance equation: A ( p 1  p 2 )  Kx
When the spool is in central position: p 1  p 2
q1
Thus
q2

A1
A2

A3
A4
1
m
7.4.1 flow divider
q0
sm all vent
p0
p1
p2
p1
A
p
p2
q1
p3
sm all vent
p 0  p 3   p I   p1
q2
p4
p 0  p 4   p II   p 2
if p3 was higher than p4, the spool would slide to the right to add
resistance to this path. This equalizes the resistance of each path,
thereby ensuring that equal flow will go to each path.
Synchronous error
2q q
 
3
q0
4
 100 %
The synchronous error of the flow dividers is less than 5%.
7.5.1 Cartridge valve
A cartridge valve is designed to be assembled into a cavity of
a ported manifold block in order to perform the valve’s intended
function.
7.5.1.1 operation principle of cartridge valve
cover plate
valve pocket
pK K
K
spring
B
pB
spool
B
A
pA
cartridge body
A
A and B are the only ports in the working line. K is the
control port ( connecting with pilot valve).
7.5.1 Cartridge valve
cover plate
valve pocket
pK K
K
spring
B
pB
spool
B
A
pA
cartridge body
A
When no hydraulic force acting on K port, the upward hydraulic
force acting on the spool is larger than spring force, spool shifts, A
and B are connected.
When there is hydraulic force acting on K, A & B disconnects
Cartridge valves allow to pass a substantial flow rate(1000L/min).
Cartridge valves integrated with all kinds of pilot valves act as
direction valve , pressure valve and flow valve.
7.5.1.2 direction control cartridge valves
Figure 7.14 the cartridge valve used as the direction control valve
(a) unidirectional valve
(b) 2 way 2 position valve
(c) 3 way 2 position valve
(d) 4 way 2 position valve
7.5.1.3 pressure control cartridge valves
Figure 7.15 the cartridge valve used as the pressure control valve
( a) relief valve
(b) solenoid relief valve
7.5.2.2 electro-hydraulic proportional relief valves
The pilot proportional relief valve can be got by using
proportional solenoid to replace the spring force in the pilot
valve of pilot relief valve.
7.5.2.3 proportional direction flow control valve
The valve can be built by using the proportional solenoid to
replace the ordinary solenoid in the solenoid direction control
valve.
The spool not only can change position, but also can change
stroke continuously or proportionally, the area of flow path
which connects ports can be changed continuously or
proportionally.
displace sensor
valve body
proportional
solenoid
spool
7.5.3 electro-hydraulic servo valves
The electro-hydraulic servo valves are more precise and have
more rapid response than electro-hydraulic proportional valves.
The electro-hydraulic servo valves are mainly used in high
speed closed loop hydraulic control system, the proportional
valves are mainly used in relatively low speed open loop control
system.
Most electro-hydraulic servo valves are two stage valves.
To flow servo valves, the displacement xp of the main spool is
proportional to input current signal I.
In order to guarantee position control of the main spool, the
position negative feedback is used between main valve and pilot
valve.
There are two forms of position feedback: direct position
feedback and position-force feedback.
7.5.3.1 direct position feedback electro-hydraulic servo valves
7.5.3.1 direct position feedback electro-hydraulic servo valves
The pilot valve is driven by the coil of moving coil force
motor directly.
The input current of the force motor is about 0~300mA.
When input current I= 0, the driven force of the force motor
coil Fi =0, the pilot spool stays at zero position.
when the input current is increased, I=300mA, the driven
force of the force motor coil will be increased to 40N, this force
exerted on the spring of the force motor, the pilot spool will
move and the displacement will be 4mm;
when changing the direction of the input current, I= -300Ma,
the pilot spool will move in opposite direction and the
displacement will be –4mm.
These shows that the displacement xspool of the pilot spool is
proportional to input current I.
7.5.3.2 Electric-hydraulic servo valve with nozzle
flapper valve and force feedback
s
ps
d0
q1
p1
q3
dn
q2
qL
x0
p2
q4
qL
x0
(a)
q3
q1
ps
qL
p1
p2
负载
q2
q4
（ b）
figure 7.24 prestage consists of the double nozzle flapper valve
7.5.3.3 the application of electro-hydraulic servo valve