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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