Komatsu F30791, Shop Manual

Page: 103 / 298

3. During fine control (when the lever is returned)
When disc (5) starts to be returned, spool (1) is
pushed up bythe force of centering spring (3) and
the pressure at port P1 .
When this happens, fine control hole f is connected
to drain chamber D and the pressure oil at port P1
is released.
If the pressure at port
P1 drops too far, spool (1) is
pushed down bymetering spring (2), and fine con-
trol hole f is shut off from drain chamber D . At al-
most the same time, it is connected to pump pres-
sure chamber P
P
, and the pump pressure is sup-
plied until the pressure at port P1 recovers to a
pressure that corresponds to the lever position.
When the spool of the control valve returns, oil in
drain chamber D flows in from fine control hole f '
in the valve on the side that is not working.
The oil passes through port P2 and enters chamber
B to fill the chamber with oil. (Fig. 3)
4. At full stroke
When disc (5) pushes down piston (4), and retainer
(7) pushes down spool (1), fine control hole f is shut
off from drain chamber D , and is connected with
pump pressure chamber P
P
. Therefore, the pilot
pressure from the control pump passes through fine
control hole f and flows to chamber A from port P1 ,
and pushes the control valve spool.
The oil returning from chamber B passes from port
P2 through fine control hole f ' and flows to drain
chamber D . (Fig. 4)
10-85
PC20R-8 PC27R-8
RKP01111
A
Control valve
B
1
T
P
f
D
P
2
P
1
4
5
3
2
P
P
f
FIG. 3
RKP01121
A
Control valve
B
1
T
P
f
D
P
2
P
1
4
5
9
P
P
f
FIG. 4