STRUCTURE, FUNCTION, & MAINTENANCE STANDARD HYDRAULIC PUMP 12 b. When load on actuator is large and pump dis- charge pressure is high When the load is large and pump discharge pres- sures PP1 and PP2 (see page 10-33) are high, the force pushing spool (3) to the left becomes larger and spool (3) moves to the position in the dia- gram above. When this happens, as shown in the diagram above, part of the pressurized oil from port B flows out through port C where the LS valve is actuated to port D , and the pressurized oil flowing from port C to the LS valve becomes approximately half of main pump pressure PP.
When port E and port G of the LS valve are con- nected (see (1) LS valve), the pressure from port J enters the large diameter end of servo piston (9), and servo piston (9) stops. If main pump pressure PP increases further and spool (3) moves further to the left, main pump pressure PP1 flows to port C and acts to make the discharge amount the minimum. When piston (9) moves to the left, springs (4) and (6) are com- pressed and push back spool (3). When spool (3) moves to the left, the opening of port C and port D becomes larger. As a result, the pressure at port C (= J ) drops, and piston (9) stops moving to the left.
The position in which piston (9) stops when this happens is further to the left than the position when pump pressures PP1 and PP2 are low. 10-44 PC210/240-7K