STRUCTURE AND FUNCTION HYDRAULIC PUMP 4) When servo piston is balanced Let us take the area receiving the pressure at the large diameter end of the piston as A1 , the area receiving the pressure at the small diam- eter end as A0 , and the pressure flowing into the large diameter end of the piston as Pen. If main pump pressure PP of the LS valve and the combined force of force Z of spring (4) and LS pressure PLS are balanced, and the relation- ship is A0 x PP = A1 x Pen , servo piston (11) will stop in that position, and the swash plate will be kept at an intermediate position.
(It will stop at a position where the openings of the throttle from port D to port E and from port C to port D of spool (6) are approximately the same.) At this point, the relationship between the area receiving the pressure at both ends of piston (11) is A0 : A1 = 1 : 2, so the pressure applied to both ends of the piston when it is balanced be- comes PP : Pen = 1.75 : 1. The position where spool (6) is balanced and stopped is the standard center, and the force of spring (4) is adjusted so that it is determined when PP - PLS = 2.1 MPa {21.5 kg/cm 2 }.
How- ever, if PSIG (the output pressure of 0 2.9 MPa {0 30 kg/cm 2 } of the EPC valve of the LS valve) is applied to port G , the balance stop position will change in proportion to pressure PSIG between PP - PLS = 2.1 0.64 MPa {21.5 6.5 kg/cm 2 }. 10-48