STRUCTURE, FUNCTION, & MAINTENANCE STANDARD HYDRAULIC PUMP 12 b. When main pump load is heavy In the same way as in the previous item, when the emergency pump drive switch is ON , the com- mand current sent to PC-EPC valve solenoid (1) becomes constant. For this reason, the force of piston (2) pushing spool (3) is constant. If main pump pressures PP1 and PP2 increase, spool (3) moves further to the left than when the main pump load is light, and is balanced at the position in the diagram above.
In this case, the pressure from port B flows to port C , so servo piston (9) moves to the left (to make the discharge amount smaller) by the same mechanism as explained in item 2)-b, and stops at a position to the left of the position when the load on the pump is light. In other words, even when the emergency pump drive switch is ON , the curve for the pump pressure PP and discharge amount Q is determined as shown in the diagram for the valve of the current sent to the PC-EPC valve solenoid through the resistor. The curve when the PC prolix switch is ON is curve ➁ , which is to the left of curve ➀ for when the pump controller is normal. PC210/240-7K 10-47