STRUCTURE, FUNCTION, & MAINTENANCE STANDARD HYDRAULIC PUMP 12 SDP08886 3) Operation in decrease direction for pump dis- charge amount The following explains the situation if the servo pis- ton (12) moves to the left (the discharge amount becomes smaller). When LS differential pressure PLS becomes larger (for example, when the area of opening of the control valve becomes smaller and pump pressure PP rises), pump pressure PP pushes spool (6) to the left. When spool (6) moves, main port pressure PP flows from port C and port D and from port K , it enters the large diameter end of the piston.
Main pump pressure PP also enters port J at the small diameter end of the piston, but because of the differ- ence in area between the large diameter end and the small diameter end of servo piston (12), servo piston (12) is pushed to the left. As a result, the swash plate moves in the direction to make angle smaller. If LS selection pressure PSIG enters port G , it acts to make the set pressure of spring (4) weaker. PC210/240-7K 10-39