Komatsu Galeo PC138US-8 Shop Manual page 119

10 Structure, function and maintenance standard
PC valve
PA : Pump port
PA2 : Pump pressure pilot port
PDP : Drain port
PM : Mode selector pressure pilot port
PPL : PC control pressure output port
PPL2: LC control pressure output port
Function
When the pump discharge pressure (PP1)
q
(check valve output pressure) and (PP2) (shut-
tle valve output pressure) are high, the PC
valve controls the pump so that the volume of
oil beyond the discharge pressure-based spe-
cific flowrate may not be conducted however
you may increase the control valve stroke.
Namely it is intended at controlling the horse
power for the pumps so that it may not exceed
the engine hose power.
If the pump discharge pressure (PP1) increases
q
due to increased load during operation, this
valve decreases the pump delivery.
And if the pump delivery pressure goes low, it
q
increases the pump delivery.
In this case, relation between the mean average
q
discharge pressure of the pump [(PP1) +
(PP2)]/2 and the pump delivery (Q) will
becomes as shown in the diagram if the relation
is represented as the parameter of the current
value to be given to PC-EPC valve solenoid.
The controller continues counting the actual
q
engine speed.
If the engine speed is slowed down due to
q
increased load, the controller reduces the
pump delivery to recover the speed.
PC138US, USLC-8
1. Plug
2. Servo piston assembly
3. Pin
4. Spool
5. Retainer
6. Sheet
7. Cover
8. Wiring
If the engine speed goes below the specified
q
value because of increased load, the controller
sends a command current to PC-EPC valve
solenoid in order to reduce the slope angle in
proportion to reduction in the engine speed.
SEN02548-01
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