STRUCTURE, FUNCTION, & MAINTENANCE STANDARD HYDRAULIC PUMP 12 SDP08885 2) Operation in increase direction for pump dis- charge amount When the difference between the main pump pressure PP and LS pressure PLS , in other words, LS differen- tial pressure PLS, becomes smaller (for example, when the area of opening of the control valve becomes larger and pump PP drops), spool (6) is pushed to the right by the combined force of LS pres- sure PLS and the force of spring (4). When spool (6) moves, port D and port E are joined and connected to the PC valve. When this happens, the PC valve is connected to the drain port, so circuit D - K becomes drain pressure PT .
(The operation of the PC valve is explained later). For this reason, the pressure at the large diameter end of servo piston (12) becomes drain pressure PT , and pump pressure PP enters port J at the small diameter end, so servo piston (12) is pushed to the right. There- fore, the swash plate moves in the direction to make the discharge amount larger. If the output pressure of the EPC valve for the LS valve enters port G , this pressure creates a force to move piston (7) to the left. If piston (7) is pushed to the left, it acts to make the set pressure of spring (4) weaker, and the difference between PLS and PP changes when ports D and E of spool (6) are connected. 10-38 PC210/240-7K