Komatsu ecot3 PC300LC-8 Shop Manual page 178

SEN01994-01
Lift check valve
Function
q This valve applies back pressure to the drain
circuit to prevent generation of negative pres-
sure on each actuator (motors, cylinders, etc.).
Operation
1. While engine is stopped
Pressurized oil is not fed to the self pressure
q
reducing valve from the pump, and valve (1) is
pressed to the right by the force of spring (2).
Drain circuit (a) of the control valve is con-
q
nected with port (T) through orifice (b) of valve
(1).
52
10 Structure, function and maintenance standard
2. While engine is running
q Output pressure (PR) of the self pressure
reducing valve is applied via the control valve
to spring chamber (c) of back pressure valve
(3).
q Output pressure (PR) applied to spring cham-
ber (c) is applied to the left end of valve (1)
φ
(area of d) to push valve (1) to the right.
q At this time, pressure (PA) of drain circuit (a) of
the control valve is applied to the right end of
valve (1) (area of
left.
q Valve (1) strikes balance to make the back
pressure equal to (PA) in the equation below.
φ
(Area of d) x PR + force of spring (2)
PA =
Area of
φ
d1) to push valve (1) to the
φ
d1
PC300, 350-8