Komatsu PC20R-8 Shop Manual page 74

1. Unload valve
FUNCTION
1) When the control valve is at HOLD, pump discharge amount Q discharged by the minimum swash plate angle is
released to the tank circuit. When this happens, pump discharge pressure P
spring (2) inside the valve.
(LS pressure P =0 bar (0 kg/cm
LS
S
1
OPERATION
When control valve is at HOLD
. At the left end of spool (1), pump pressure P
ing on area S1, and at the right end of spool (1),
pump pressure P is acting on area S2, and LS
P
pressure P is acting on area S3.
LS
. When the control valve is at HOLD, LS pressure
P is not generated, so only pump discharge P
LS
has any effect, and P
(2).
. As pump discharge pressure P
the P x S1=P x S2+spring force of spring (2),
P P
spool (1) is moved to the right.
Pump circuit P is then connected to tank circuit T
P
through the drill hole.
. In this way, pump discharge pressure P
2
16 bar (16 kg/cm ).
10-56
2
)
1
P
A T
is act-
P
is set by the load of spring
P
rises and reaches
P
is set to
P
P
P
2
P =Pump circuit
P
P =LS circuit
LS
T =Tank circuit
A =To valves
B =To pump LS valve
P
is set to 16 bar (16 kg/cm
P
B
LS
T
PC20R-8 PC27R-8
2
) by
S S
3 2
RKP00720