Chapter 7 Flow Control Valves and Other Chapter 7 Flow Control Valves and Other Hydraulic ValvesHydraulic 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

T( )mq CA p )15.0( m

q

pΔq 2

Δq 1

Conclusion: Thin-wall orifices should be used for throttle orifices

7.1 Throttle valves

Figure 7.2 throttle valve Figure 7.3 throttle valve with a with axial vee notch orifice spiral curve and thin bladed notch 1.top cover 2.guide sleeve 1.hand wheel 2.spool 3. valve body 4.spool 3. valve pocket 4. valve body 5.spring 6.bottom cove

2 structure

7. 2 combined flow control and check valves

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.

2 Measure methods of some physical parameters

0 1 2 0 1 2 0( ) ( ) ( ) ( ) ( )pA k x x p p A k x x p p A k x x (1) pressure measure (b) pressure sum measure (c) pressure difference measure

How to remove the influence?

The solution is to add a correction loop.

7.3 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.

3 construction of a 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

1 2 3( ) ( ) ( )Txpp

p p p

4 flow path

pressure drop of the pressurere ducing valvepressure drop of the throttle valve

x

T

pp

5 measure and control quantityThe pressure drop of the throttle valve Tp

7.3 Flow regulating valve

Equilibrium equation ΣF=K(x0+x)+p3A –p2A=0

6 static equation

7.3 Flow regulating valve

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

p1≈constant p2= p1-Δpx

3 2 2 31

3 2 2 3

((

x

x

Load p x p p p p Cq const

Load p x p p p p C

））

8 Application The valve is usually used to adjust or stabilize velocity.

7.3 Flow regulating valve

7 Transient regulation

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.

7.3 Flow regulating valve

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

figure 7.9 the operation principle of the flow dividers1,2 – fixed orifices 3,4- the adjustable orifices 5- valve body6- reducing pressure valve 7- spring

Throttle equation: Balance equation:When the spool is in central position:

Thus

1 1 0 1 2 2 0 2( ) ( )m mq CA p p q CA p p KxppA )( 21

21 pp

14

3

2

1

2

1 A

A

A

A

q

q

7.4.1 flow divider

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 The synchronous error of the flow dividers is less than 5%.

%1002

0

43

q

qq

0 3 I 1 0 4 II 2 p p p p p p p p

7.4.1 flow divider

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

A and B are the only ports in the working line. K is the control port ( connecting with pilot valve).

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 Cartridge valve

7.5.1.2 direction control cartridge valves 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 valves7.5.1.3 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 7.5.2.2 electro-hydraulic proportional relief valves

The pilot proportional relief valve can be got by using The pilot proportional relief valve can be got by using proportional solenoid to replace proportional solenoid to replace the spring force in the pilot in the pilot valve of pilot relief valve. 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.

7.5.3 electro-hydraulic servo valves7.5.3 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 The electro-hydraulic servo valves are mainly used in high speed closed loop hydraulic control system, the proportional speed closed loop hydraulic control system, the proportional valves are mainly used in relatively low speed open loop control valves are mainly used in relatively low speed open loop control system. system. Most electro-hydraulic servo valves are two stage valves. Most electro-hydraulic servo valves are two stage valves. To flow servo valves, the displacement To flow servo valves, the displacement xxpp of the main spool is of the main spool is

proportional to input current signal I. proportional to input current signal I. In order to guarantee position control of the main spool, the pIn order to guarantee position control of the main spool, the position negative feedback is used between main valve and pilot vosition negative feedback is used between main valve and pilot valve. alve. There are two forms of position feedback: direct position feedbThere are two forms of position feedback: direct position feedback and position-force feedback.ack and position-force feedback.

7.5.3.1 direct position feedback electro-hydraulic servo valves7.5.3.1 direct position feedback electro-hydraulic servo valves

7.5.3.1 direct position feedback electro-hydraulic servo valves7.5.3.1 direct position feedback electro-hydraulic servo valves

The pilot valve is driven by the coil of moving coil force motoThe pilot valve is driven by the coil of moving coil force motor directly. r directly. The input current of the force motor is about 0~The input current of the force motor is about 0~300mA. 300mA. When input current When input current II= 0, the driven force of the force motor = 0, the driven force of the force motor coil coil FFi i =0, the pilot spool stays at zero position.=0, the pilot spool stays at zero position.

when the input current is increased, when the input current is increased, II=300mA, the driven for=300mA, the driven force of the force motor coil will be increased to 40N, this force exce 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 erted on the spring of the force motor, the pilot spool will move and the displacement will be 4mm;and the displacement will be 4mm; when changing the direction of the input current, when changing the direction of the input current, II= -300Ma, = -300Ma, the pilot spool will move in opposite direction and the displacethe pilot spool will move in opposite direction and the displacement will be –4mm.ment will be –4mm. These shows that the displacement These shows that the displacement xxspoolspool of the pilot spool is p of the pilot spool is p

roportional to input current roportional to input current II..

7.5.3.2 Electric-hydraulic servo valve with nozzle 7.5.3.2 Electric-hydraulic servo valve with nozzle flapper valve and force feedbackflapper valve and force feedback

figure 7.24 prestage consists of the double nozzle flapper valvefigure 7.24 prestage consists of the double nozzle flapper valve

7.5.3.3 the application of electro-hydraulic servo valve7.5.3.3 the application of electro-hydraulic servo valve