STRUCTURE AND FUNCTION HYDRAULIC PUMP 3) Operation in minimum direction for pump discharge amount The following explains the situation if servo pis- ton (11) moves to the left (the discharge amount becomes smaller). When LS differential pres- sure PLS becomes larger (for example, when the area of opening of the control valve be- comes smaller and pump pressure PP rises), the force produced by pump pressure PP pushes spool (6) to the left. When spool (6) moves, main pump pressure PP flows from port C to port D , and it enters the large diameter end of the piston from port K .
Main pump pressure PP also enters port J at the small diameter end of the piston, but be- cause of the difference in area between the large diameter end and the small diameter end of servo piston (11), servo piston (11) is pushed to the left. As a result, the swash plate moves in the direc- tion to make angle smaller. If LS selection pressure PSIG enters port G, it acts to make the set pressure of spring (4) weaker. 10-47