Komatsu F30791, Shop Manual

Page: 77 / 298

2. Introduction of LS pressure
FUNCTION
. The LS pressure is the actuator load pressure at the outlet port end of the control valve.
. It actuallyreduces pump pressure P
P
at reducing valve (3) of the pressure compensation valve to the same pres-
sure as actuation circuit pressure A , and sends it to the LS circuit P
LS
.
. With the boom swing and blade valves, pump pressure P
P
is reduced to the same pressure as actuator circuit
pressure A byone reducing valve (3) used for both systems, and the pressure is sent to the LS circuit P
LS
.
OPERATION
1) Boom, arm, bucket, travel valve
. When spool (1) is operated, pump pressure P
P
flows from control valve (2) and notch a in spool
(1) through bridge passage b to actuator circuit A .
. At the same time, reducing valve (3) also moves to
the right, so pump pressure P
P
has its pressure re-
duced bythe pressure loss at notch C . It is intro-
duced to LS circuit P
LS
, and then goes to spring
chamber P
LS1
.
. When this happens, LS circuit P
LS
is connected to
tank circuit T from LS by-pass plug (4) (see the sec-
tion on the LS by-pass plug).
. Actuator circuit pressure P
A
(= A ) acts on the left
end of reducing valve (3); the reduced pump pres-
sure P
P
acts on the other end.
. As a result, reducing valve (3) is balanced at a po-
sition where actuator circuit pressure P
A
and the
pressure of spring chamber P
LS1
are the same.
Pump pressure P
P
reduced at notch C becomes ac-
tuator circuit pressure A and is taken to LS circuit
P
LS
.
10-59
PC20R-8 PC27R-8
RKP00392
1
2
3
4
A
a b
T
P
A
P
LS1
P
LS
T
C
P
P
To PPC valve
From PPC valve