Komatsu Galeo PC800-8 Shop Manual page 210

SEN00384-02
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).
2. During 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, 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 to re-
lease the pressure at port P1.
• 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 in the position of spool (1) and
body (10) (fine control hole f is in the middle be-
tween drain hole D and pump pressure chamber
PP) does not change until retainer (9) contacts
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 control valve spool 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.
48
10 Structure, function and maintenance standard
PC800, 850-8