Komatsu PC88MR-10 Shop Manual page 157

Unload valve
(PC88MR-PQD5-041-K-00-A)
When control valve is in HOLD position
Function
This valve drains discharged volume (Q) for the minimum pump swash plate angle into the tank circuit
when the control valve is held.
Pump discharged pressures (PP1) and (PP2) are set to 2.45 MPa {25.0 kg/cm
[LS pressures (PLS1) and (PLS2) are 0 MPa {0 kg/cm
Since the merge-divider spool is at the merge position, pump discharged pressures (PP1) and (PP2) are
merged.
LS pressures (PLS1), (PLS2), and (PLS3) are merged.
Operation
Pump discharged pressures (PP1) and (PP2) act on the right side of unload spool (1), and LS pressures
(PLS1) and (PLS2) act on the left side. (PP1 = PP2, PLS1 = PLS2)
When the control valve is held, only pump discharged pressures (PP1) and (PP2) are applied since LS
pressures (PLS1) and (PLS2) are 0 MPa {0 kg/cm
(PP1) and (PP2) are set only by the load at installed height of spring (2).
Pump discharged pressures (PP1) and (PP2) increase and reach the load at installed height of spring (2)
(2.45 MPa {25.0 kg/cm
Spool (1) moves to the left.
Pump circuits (PP1) and (PP2) are connected to tank circuit (T) through the notch of spool (1).
Pump discharged pressures (PP1) and (PP2) are set to 2.45 MPa {25.0 kg/cm
PC88MR-10
2 }).
10 Structure and function
2 }]
2 }.
Control valve
} by spring (2) in the valve.
2
2 }.
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