STRUCTURE, FUNCTION, & MAINTENANCE STANDARD HYDRAULIC PUMP 12 2) When pump controller is abnormal and PC prolix switch is ON a. When load on main pump is light If there is a failure in the pump controller, turn emergency pump drive switch ON to switch to the resistor side. In this case, the power source is taken directly from the battery. But if the current is used as it is, it is too large, so use the resistor to control the current flowing to PC-EPC valve solenoid (1). When this is done, the current becomes constant, so the force pushing piston (2) is also constant.
If the main pump pressure PP1 and PP2 are low, the combined force of the pump pressure and the force of PC-EPC valve solenoid (1) is weaker than the spring set force, so spool (3) is balanced at a position to the left. At this point, port C is connected to the drain pressure of port D , and the large diameter end of the piston of servo piston (9) also becomes the drain pressure PT through the LS valve. When this happens, the pressure at the small diameter end of the piston is large, so servo piston (9) moves in the direction to make the discharge amount larger. 10-46 PC210/240-7K