Komatsu Galeo PC138US-8 Shop Manual page 187

10 Structure, function and maintenance standard
Operation
1. When in neutral
Ports (A) and (B) of the control valve and ports
q
(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
o
(Neutral fine control)
When piston (4) is pushed by disc (5), retainer
q
(9) is pushed, spool (1) is also pushed by
metering spring (2), and moves down.
When fine control hole (f) is shut off from drain
q
chamber (D), it is almost simultaneously inter-
connected to pump pressure chamber (PP).
Pilot pressurized oil of the control pump is led
q
to port (A) from port (P1) through fine control
hole (f).
When the pressure at port (P1) becomes
q
higher, spool (1) is pushed back and fine con-
trol hole (f) is shut off from pump pressure
chamber (PP). At almost the same time, it is
connected to drain chamber (D) to release the
pressure at port (P1).
As a result, spool (1) moves up and down until
q
the force of metering spring (2) is balanced
with the pressure at port (P1).
PC138US, USLC-8
The relationship of the position of spool (1) and
q
body (10) [fine control hole (f) is in the middle
between drain chamber (D) and pump pres-
sure chamber (PP)] does not change until
retainer (9) contacts spool (1).
Metering spring (2) contracts in proportion to
q
the stroke of the control lever.
Pressure at port (P1) also rises in proportion to
q
the stroke of the control lever.
In this way, the control valve spool moves to a
q
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.
SEN02550-01
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