Komatsu Galeo PC138US-8 Shop Manual page 154

SEN02549-02
Unload valve
1. When control valve is at HOLD
Function
When the control valve is at HOLD, pump
q
delivery (Q) discharged by the minimum swash
plate angle is released to the tank circuit. At
this time, pump discharge pressure (P1) and
(P2) is set by spring (2) in the valve. [LS pres-
sure (LS1) and (LS2) = 0 MPa {0 kg/cm²}]
Since the pump merge-divider valve is at the
q
merge position, pump discharge pressures
(P1) and (P2) are merged. LS pressures (LS1),
(LS2), and (LS3) are also merged.
Operation
Pump discharge pressures (P1) and (P2) are
q
applied to pump pressure receiving (SA) face
of unload spool (1).
LS pressures (LS1) and (LS2) are applied to
q
LS pressure receiving (SB) face. [(P1) = (P2),
(LS1) = (LS2)]
20
10 Structure, function and maintenance standard
When the control valve is at HOLD, LS pres-
q
sures (LS1) and (LS2) are not generated, so
only pump discharge pressures (P1) and (P2)
act, and (P1) and (P2) are set by only the load
of spring (2).
As pump discharge pressure (P1) and (P2)
q
rises and reaches the load of spring (2), spool
(1) is moved to the left. Pump discharge pres-
sures (P1) and (P2) are connected to tank cir-
cuit (T) through the notch of spool (1).
PC138US, USLC-8