Komatsu Galeo PC138US-8 Shop Manual page 126

SEN02548-01
2. As the emergency pump drive switch is turned on due to failure on the pump
controller
1) When the main pump is under light load
If there is a failure in the pump controller, the
q
emergency pump drive switch is turned on to
hand the control to the resistor side.
In this case, the power is directly supplied from
q
the battery. The current, however, is too large
as is, so the resistor is set in between to con-
trol the current flowing to PC-EPC valve sole-
noid (1).
The current becomes constant, so the force
q
pushing piston (2) is also constant.
26
10 Structure, function and maintenance standard
If the main pump pressures (PP1) and (PP2)
q
are low, the combined force of the pump pres-
sure and the PC-EPC valve solenoid (1) is
weaker than the spring set force, so spool (3)
is balanced at a position to the right.
The port (C) is connected to the drain pressure
q
of the port (D), and the large diameter end of
the servo piston (9) also becomes the drain
pressure (PT) through the LS valve.
Since the pressure on the small diameter end
q
of the piston is large, servo piston (9) moves in
the direction to make the delivery larger.
PC138US, USLC-8