Komatsu Galeo PC138US-8 Shop Manual page 127

10 Structure, function and maintenance standard
2) When the main pump is under heavy load
If the emergency pump drive switch is turned
q
on in the same way as in above, the command
current (X) sent to PC-EPC valve solenoid (1)
becomes constant.
For this reason, the force of piston (2) pushing
q
spool (3) is constant.
If main pump pressures (PP1) and (PP2)
q
increase, spool (3) moves further to the left
than when the main pump load is light, and is
balanced at the position in the figure above.
In this case, the pressure from port (A) flows to
q
port (C), so servo piston (9) moves to the left
(smaller pump delivery) and stops at a position
to the further to the left then when the load on
the pump is light.
PC138US, USLC-8
SEN02548-01
27