Komatsu Galeo PC138US-8 Shop Manual page 180

SEN02549-02
Self pressure reducing valve
Function
The self pressure reducing valve lowers the
q
discharge pressure of the main pump and sup-
plies it as the control pressure for the solenoid
valves, PPC valves, etc.
Operation
If the (PR) pressure rises higher than the set
q
level, poppet (1) opens and the hydraulic oil
flows from port (PR) through orifice (a) in spool
(4) and opening of poppet (1) into seal drain
port (TS).
Accordingly, differential pressure is generated
q
over orifice (a) in spool (4) and spool (4)
moves in the direction to close the opening
between ports (P) and (PR). The (P) pressure
is lowered and controlled to a constant pres-
sure (set pressure) by the opening ratio at this
time and supplied as the (PR) pressure.
46
10 Structure, function and maintenance standard
When abnormally high pressure is generated
If the (PR) pressure of the self pressure reduc-
q
ing valve is raised abnormally, ball (6) sepa-
rates from the seat against the force of spring
(5). As a result, the hydraulic oil flows from
output port (PR) to (TS) and the (PR) pressure
lowers.
Accordingly, the devices receiving the oil pres-
q
sure (PPC valves, solenoid valves, etc.) are
protected from abnormally high pressure.
PC138US, USLC-8