Chapter 8 Flow control

valves

— limiting the fluid volume flow rate from fixed displacement pumps accurately. — Applications: velocity control of cylinders; speed control of hydraulic motors — ; where Q : volume flow rate to actuator A : effective area of cylinder piston V : displacement of hydraulic motor

§ Type of flow control valves 1) Throttle valves Non-variable restriction variable restriction(i.e. adjustable) —

A

Qv

VQ

n

PQ

2) Pressure compensated flow control valve Basic idea : Q constant , indep. of change in P

Principle of operation :

Neglecting flow force , obtaining the eq. of force equilibrium on the pressure compensator: P1 A=PL A + Ff

P = P1 – PL =

(B)meter-out

(Ps – PL)A= P1 A + Ff

P = (Ps – PL ) – P1=

Q constant

constAFf

∵Ff =k(x0 – x ) 且 x << x0

(x0 : Pre-compression)

constAFf

— static performance

E4 : due to flow force at large Q

E1 : due to the characteristic of the

original throttle PQ

流量控制閥：

(2) 節流閥 (Throttle valve)

(3) 數種常見之節流口

1) 節流閥： ( 具備 free reverse flow)

2) 壓力補償式流量控制閥特性圖：

3) 壓力 , 溫度補償式流量控制閥：

§ 二通流量控制閥與三通流量控制閥之比較： (two-way) (three-way)

(a)Two-way: ( 壓力補償桿與節流閥串聯 )

(b)Three-way: ( 壓力補償桿與節流閥並聯 )

減速閥 (deceleration valve) ：

(a) 結構及工作原理

(b) 減速回路及 symbols

分流閥 (flow divider valves)

(a)Flow divider valve with equal flow division

(b)Priority flow divider valve