STRUCTURE AND FUNCTION HYDRAULIC PUMP OPERATION 1. LS VALVE 1) When control valve is at neutral position The LS valve is a three-way selector valve. with pressure PLS (LS pressure) from the inlet port of the control valve brought to spring chamber B , and main pump dis- charge pressure PP brought to port H of sleeve (8). The size of the force produced by this LS pressure PLS + force Z of spring (4) and the main pump pressure (self-pressure) PP determines the position of spool (6). However, the size of the output pressure PSIG (the LS selection pressure) of the EPC valve for the LS valve entering port G also changes the position of spool (6).
(The set pressure of the spring changes.) Before the engine is started, servo piston (11) is pushed to the right (large diameter end). (See the diagram on the right.) When the engine is started and the control lever is at the neutral position, LS pressure PLS is 0 MPa {0 kg/cm 2 }. (It is intercon- nected with the drain circuit through the control valve spool.) At this point, spool (6) is pushed to the left, and port C and port D are connected.
Pump pressure PP enters the large diam- eter end of the piston from port K , and the same pump pressure PP also enters port J at the small diameter end of the piston, so the swash plate is moved to the minimum angle by the difference in area of piston (11). 10-45