Komatsu Galeo PC138US-8 Shop Manual page 181

10 Structure, function and maintenance standard
Lift check valve and cooler bypass valve
Lift check valve
Function
The lift check valve generates back pressure in
q
the drain circuit to prevent negative pressure
on each actuator (motor, cylinder, etc.)
Operation
Drain circuit pressure (PA) of the control valve
q
acts on the left side of piston (2) to move the
piston to the right.
The piston is so balanced that the back pres-
q
sure will be as follows.
(PA) – (PB) = Force of spring (3) / Area of pis-
q
ton (2) at diameter (d1)
[(PB) C 0 kg/cm²]
PC138US, USLC-8
Cooler bypass valve
Function
The cooler bypass valve protects oil cooler (4)
q
from breakage when the return flow rate from
the control valve increases and oil cooler inlet
pressure (PB) increases.
The cooler bypass valve returns the return oil
q
to the tank directly without passing it through
oil cooler (4).
Operation
Oil cooler inlet pressure (PB) acts on the
q
underside of piston (1) to push up the piston.
Piston (1) is so balanced that oil cooler inlet
q
pressure (PB) will be as follows.
(PB) – (PT) = Force of spring (5) / Area of pis-
q
ton (1) at diameter (d2)
[(PT) C 0 kg/cm²]
SEN02549-02
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