Komatsu Utility PC12R-8 MISTRAL, Shop Manual

Page: 94 / 324

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
P
is set to 19.6
9.8
bar (20
10
kg/
cm
2
) by spring (2) inside the valve.
( LS pressure P
LS
=0 bar (0 kg/cm
2
)
OPERATION
When control valve is at HOLD
. At the left end of spool (1), pump pressure P
P
is ac-
ting on area S1 , and at the right end of spool (1),
pump pressure P
P
is acting on area S2 , and LS
pressure P
LS
is acting on area S3 .
. When the control valve is at HOLD, LS pressure
P
LS
is not generated, so only pump discharge P
P
has any effect, and P
P
is set by the load of spring
(2).
. As pump discharge pressure P
P
rises and reaches
the P
P
x S1 = P
P
x S2 +spring force of spring (2),
spool (1) is moved to the right.
Pump circuit P
P
is then connected to tank circuit T
through the drill hole.
. In this way, pump discharge pressure P
P
is set to
19.6
9.8
bar (20
10
kg/cm
2
).
P
P
=Pump circuit
P
LS
=LS circuit
T =Tank circuit
A =To valves
B =To pump LS valve
10-76
PC12R-8 PC15R-8
RKP00720
1
P
P
B S
3
S
2
T T
A
S
1
2
P
LS