Komatsu F30791, Shop Manual

Page: 105 / 298

FUNCTION
1. At neutral
Ports A and B of the control valve and ports P1 and
P2 of the PPC valve are connected to drain cham-
ber D through fine control hole f in spool (1). (Fig. 1)
2. During fine control (NEUTRAL fine control)
When piston (4) starts to be pushed bylever (5), re-
tainer (7) is pushed; spool (1) is also pushed byme-
tering spring (2), and moves down.
When this happens, fine control hole f is shut off
from drain chamber D , and at almost the same
time, it is connected to pump pressure chamber
P
P
, so pilot pressure oil from the control pump
passes through fine control hole f and goes from
port P1 to port A .
When the pressure at port P1 becomes higher,
spool (1) is pushed back and fine control hole f is
shut off from pump pressure chamber P
P
.
At almost the same time, it is connected to drain
chamber D to release the pressure at port P1 .
When this happens, spool (1) moves up or down so
that the force of metering spring (2) is balanced with
the pressure at port P1 . The relationship in the po-
sition of spool (1) and body(8) (fine control hole f is
at a point midwaybetween drain hole D and pump
pressure chamber P
P
) does not change until retai-
ner (7) contacts spool (1).
Therefore, metering spring (2) is compressed pro-
portionallyto the amount of movement of the con-
trol lever, so the pressure at port P1 also rises in
proportion to the travel of the control lever. In this
way, the control valve spool moves to a position
where the pressure in chamber A (the same as
pressure at port P1 ) and the force of the control
valve spool return spring are balanced. (Fig. 2)
10-87
PC20R-8 PC27R-8
RKP00971
A
Control valve
B
1
T
P
f
D
P1
P2
FIG. 1
RKP00981
A
B
T
P
P1
P
P
D
P2
Control valve
4
5
7
8
1
2
f
FIG. 2