Komatsu PC500LC-10R, Shop Manual, Page: 214 / 758

STRUCTURE OF MAIN PUMP PC VALVE
Sectional view
PA: Pump port
PA2: Pump pressure pilot port
PDP: Drain port PM: Mode selector pressure pilot port
PPL: Control pressure output port (to LS valve)
1: Plug
2: Servo piston assembly
3: Pin
4: Spool 5: Retainer
6: Seat
7: Cover
8: Wiring
FUNCTION OF MAIN PUMP PC VALVE
• The PC valve limits the oil flow to a certain level depending on the discharged pressure, even if the travel of
the control valve is increased extremely so that the horsepower absorbed by the pump does not exceed the
engine horsepower, when pump discharged pressures (PP1) (self pressure) and (PP2) (the other pump
pressure) are high.
• When the load increases and the pump discharged pressure (PP) also increases during work, the pump
discharged volume is reduced.
• When the pump discharged pressure decreases, the pump discharged volume is increased.
The relation between the average of front and rear pump
discharged pressures “(PP1) + (PP2)”/2 and pump dis-
charged volume (Q) in this case is shown in the figure be-
low by using current values (X) given to PC-EPC valve sol-
enoid as parameters.
• When the load increases and the rotation speed decreas-
es, the pump discharged volume is decreased to recover
the rotation speed.
• When the load increases and the engine speed drops be-
low the set value, the command current from the controller
to PC-EPC valve solenoid increases according to the de-
crease of the engine speed, and the pump inclination an-
gle decreases.
• The controller counts the actual engine r.p.m.
COMPONENT PARTS OF HYDRAULIC SYSTEM 10 STRUCTURE AND FUNCTION
10-120 PC500LC-10R