Komatsu PC600LC-7 Manual page 140

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
Operation
1. At neutral
Ports A and B of the control valve and ports P1
and P2 of the PPC valve are connected to drain
chamber D through fine control hole f in spool
(1). (Fig. 1)
2. Fine control (neutral
When piston (4) starts to be pushed by disc (5),
retainer (9) is pushed. Spool (1) is also pushed
by metering spring (2) and moves down.
When this happens, fine control hole f is shut off
from drain chamber D. At almost the same time,
it is connected to pump pressure chamber PP,
and the pilot pressure of the control pump is
sent from port A through fine control hole f to
port P1.
When the pressure at port P1 rises, spool (1) is
pushed back. Fine control hole f is shut off from
pump pressure chamber PP. At almost the same
time, it is connected to drain chamber D, so the
pressure at port P1 escapes. As a result, spool
(1) moves up and down until the force of meter-
ing spool (2) is balanced with the pressure of
port P1.
The relationship of the positions of spool (1) and
body (10) (fine control hole f is in the middle
between drain hole D and pump pressure cham-
ber PP) does not change until retainer (9) con-
tacts spool (1).
Therefore, metering spring (2) is compressed in
proportion to the travel of the control lever, so
the pressure at port P1 also rises in proportion
to the travel of the control lever.
In this way, the spool of the control valve moves
to a position where the pressure of chamber A
(same as pressure at port P1) and the force of
the return spring of the control valve spool are
balanced. (Fig. 2)
10-108
fine control)
WORK EQUIPMENT, SWING PPC VALVE
f
P
1
P P
1 2
A
Control valve
(Fig. 1)
5
4
9
2
f
P
1
P
1
A
Control valve
(Fig. 2)
D
T
B
SBP00275
D
T
P
P
P
2 10
B
SBP00276
PC600, 600LC-7