Komatsu PC200-8M0 Shop Manual page 135

401 Hydraulic system, Part 1
Hydraulic pump
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
q If there is a failure in the pump controller, the
emergency pump drive switch is turned on to
hand the control to the resistor side.
q In this case, the power is directly supplied from
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).
q The current becomes constant, so the force
pushing piston (2) is also constant.
q If the main pump pressures (PP1) and (PP2)
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 left.
q The port (C) is connected to the drain pressure
of the port (D), and the large diameter end of
the servo piston (9) also becomes the drain
pressure (PT) through the LS valve.
PC200, 200LC, 220, 220LC-8M0
q Since the pressure on the small diameter end
of the piston large, servo piston (9) moves in
the direction to make the discharge amount
larger.
SEN06119-00
23
10-401