STRUCTURE AND FUNCTION HYDRAULIC PUMP 2) Operation in maximum direction for pump discharge amount When the difference between main pump pres- sure PP and LS pressure PLS , in other words, LS differential pressure PLS becomes smal- ler (for example, when the area of opening of the control valve becomes larger and pump pressure PP drops), spool (6) is pushed to the right by the combined force of LS pressure 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 pres- sure PT .
(The operation of the PC valve is ex- plained later.) For this reason, the pressure at the large diam- eter end of servo piston (11) becomes drain pressure PT , and pump pressure PP enters port J at the small diameter end, so servo pis- ton (11) is pushed to the right. Therefore, 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, its acts to make the set pres- sure of spring (4) weaker, and the difference between hydraulic pressure PLS and PP changes when ports D and E of spool (6) are connected.
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