Komatsu F30791, Shop Manual

Page: 74 / 298

1. Unload valve
FUNCTION
1) When the control valve is at HOLD, pump discharge amount Q discharged bythe minimum swash plate angle is
released to the tank circuit. When this happens, pump discharge pressure P
P
is set to 16 bar (16 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 act-
ing 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 onlypump discharge P
P
has anyeffect, and P
P
is set bythe 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
16 bar (16 kg/cm
2
).
P
P
=Pump circuit
P
LS
=LS circuit
T =Tank circuit
A =To valves
B =To pump LS valve
10-56
PC20R-8 PC27R-8
RKP00720
1
P
P
B S
3
S
2
T T A S
1
2
P
LS