Komatsu PC88MR-10 Shop Manual page 163

Introduction of LS pressure
Work equipment valve: Swing, boom, arm, bucket, boom swing, attachment
Function
LS pressure is the actuator load pressure on the outlet side of the control valve.
Actually, pump pressure (PP) is reduced with pressure reducing valve (3) of the pressure compensation
valve to actuator circuit pressure (A), and then it is supplied to LS circuit (PLS).
In the travel valve, actuator circuit pressure (A) is supplied directly to LS circuit (PLS).
Operation
When spool (1) is operated, pump discharged pressure (PP) flows from flow control valve (2) and notch
(a) in the spool through bridge passage (b) to actuator circuit (A).
Since pressure reducing valve (3) moves to the right, so pump discharged pressure (PP) is reduced due
to the pressure loss at notch (c) and then transmitted through LS circuit (PLS) to spring chamber (PLSS).
LS circuit (PLS) is connected to tank circuit (T) from LS bypass valve (4). (See "LS bypass valve".)
The areas at both ends of pressure reducing valve (3) are the same [(SA) = (SLS)], and actuator circuit
pressure (PA) acts on the (SA) end. The reduced pump discharged pressure (PP) acts on (SLS) the other
end.
Pressure reducing valve (3) is balanced at a position where actuator circuit pressure (PA) and the
pressure of spring chamber (PLSS) are the same. Pump discharged pressure (PP) reduced at notch (c)
becomes actuator circuit pressure (A) and is transmitted into LS circuit (PLS).
PC88MR-10
(PC88MR-C2A4-041-K-00-A)
10 Structure and function
Control valve
10-85