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 Conclusion: q Δq2 Δq1 Conclusion: Thin-wall orifices should be used for throttle orifices

7.1 Throttle valves 2 structure 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

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. How to remove the influence? The solution is to add a correction loop. 2 Measure methods of some physical parameters (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 5 measure and control quantity

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

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%.

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).

7.5.1 Cartridge 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.

7.5.1.2 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.

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 figure 7.24 prestage consists of the double nozzle flapper valve

7.5.3.3 the application of electro-hydraulic servo valve