Komatsu PC88MR-10 Shop Manual page 137

LS valve
(PC88MR-C2J0-042-K-01-A)
The LS valve controls the pump discharged volume according to the travel of the control lever, or the flow
demanded by the actuator.
The LS valve detects the flow rate demanded by the actuator from differential pressure (dPLS) between
inlet pressure (PPLS) and outlet pressure (PLS) of the control valve and controls pump discharged
volume (Q). [(PPLS) is called LS pump pressure, (PLS) LS pressure, and (dPLS) LS differential pressure]
In other words, pressure loss [= LS differential pressure (dPLS)], which occurs when the oil flows through
the passage in control valve spool, is detected, and pump discharged volume (Q) is controlled to maintain
the pressure loss at a constant level. Through this operation, the pump can discharge the proper volume
of oil as demanded by the actuator.
Pump discharged pressure (PP), LS pump pressure (PPLS), and LS pressure (PLS) are applied to LS
valve. The relationship between LS differential pressure (dPLS) and pump discharged volume (Q)
changes as shown below.
PC valve
(PC88MR-C2K0-042-K-00-A)
The PC valve limits the oil flow to a certain level (depending on the discharged pressure) even if the travel
of the control valve is increased extremely so that the horsepower absorbed by the pump does not exceed
the engine horsepower, when pump discharged pressure (PP) is high.
The PC valve decreases the pump discharged volume when the work load is increased and the pump
discharged pressure rises, and increases it when the pump discharged pressure lowers.
This pump has 2 discharge ports and the average of respective discharged pressures (P1) and (P2) is
sensed.
The average of (P1) and (P2) is called (PAVE), and the relationship between it and the pump discharged
volume [total discharge of (P1) and (P2)] is as shown in the figure below.
PC88MR-10
10 Structure and function
Main pump
10-59