Komatsu PC20R-8 Shop Manual page 105

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
When piston (4) starts to be pushed by lever (5), re-
tainer (7) is pushed; spool (1) is also pushed by me-
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 , so pilot pressure oil from the control pump
P
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
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 midway between drain hole D and pump
pressure chamber P
P
ner (7) contacts spool (1).
Therefore, metering spring (2) is compressed pro-
portionally to 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)
PC20R-8 PC27R-8
fine control)
.
P
) does not change until retai-
D
f
1
P1
A
Control valve
5
4
7
2
f
1
P1
A
Control valve
T
P
P2
B
RKP00971
FIG. 1
D
T
8
P
P2
P
P
B
FIG. 2
RKP00981
10-87