Komatsu Galeo PC800-8 Shop Manual page 205

10 Structure, function and maintenance standard
Operation
1) At neutral
Ports A and B of the control valve and ports P1,
P2, P3, and P4 of the PPC valve are connected
to drain chamber D at the bottom.
2) Fine control (neutral o fine control)
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, port P1 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 P1 to port A.
When the pressure at port P1 rises, spool (1) is
pushed back. Port P1 is shut off from pump
pressure chamber PP. At almost the same time,
it is connected to drain chamber D, so the pres-
sure at port P1 escapes.
As a result, spool (1) moves up and down until
the force of metering spool (2) is balanced with
the pressure of port P1.
The relationship of the positions of spool (1) and
body (10) 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.
PC800, 850-8
SEN00384-02
43