Komatsu F30791, Shop Manual

Page: 54 / 298

4. When pump flow is amount demanded by control valve
. Let us take the area receiving the pressure at the
large diameter end of servo piston (4) as A
1
, the
area receiving the pressure at the small diameter
end as A
2
, the pressure acting on the large piston
diameter end as P
EN
and the pressure acting on the
small piston diameter end as P
P
.
. When the flow of oil from the pump reaches the
flow demanded bythe control valve, pump pres-
sure P
P
acting on port b of the LS valve and the
combined force of LS pressure P
LS
+ force of
spring (8) acting on spring chamber a are balanced,
so piston (6) stops at almost the central position.
. As a result, port c , port d and port e open approxi-
matelythe same amount, so the pump pressure
flows from port c to port d .
Part flows from port e to the tank case and is
drained, so the pressure is reduced byapprox. 1/2
and flows to chamber X at the large diameter end
of servo piston (4).
. At this point, the relationship between the area re-
ceiving the pressure at both ends of servo piston
(4) is A
2
: A
1
= 1 : 2 , so the pressure applied to both
ends of servo piston (4) becomes P
P
: P
EN
= 2 : 1 .
This makes the force acting on both ends of servo
piston (4) 1 : 1 , so servo piston (4) stops in that po-
sition and the pump discharge amount is balanced
with the oil flow demanded bythe control valve.
10-36
PC20R-8 PC27R-8
Control valve
To actuator
LS valve
x
a b
d
RKP01231
4
P
P
M
G
H
G
L
P
LS
P
LS
c e
G
H
A
1
8 6
6
A
2
P
P