Komatsu PC500LC-10R Shop Manual page 366

COMPONENT PARTS OF TRAVEL SYSTEM
9.
The control valve spool moves to a position at which the pressure in the port (A) which is "equal to the pres-
sure in the port (P1)" is balanced with the reaction force of the return spring of the control valve spool.
When operating the fine control (when the control lever is returned)
1.
The spool (1) is pushed up by the force of centering spring
(3) and the pressure in port (P1) when lever (5) starts be-
ing returned.
2.
The fine control hole (f) is connected to the drain chamber
(D), and the pressurized oil in the port (P1) is decreased.
3.
The spool (1) is pushed down by the metering spring (2)
when the pressure in the port (P1) decreased too much.
4.
The fine control hole (f) is disconnected from the drain
chamber (D), and it is connected to the pump pressure
chamber (PP) almost simultaneously.
5.
The pump pressure is supplied until the pressure in the
port (P1) is restored to that equivalent at the lever position.
6.
When the spool of control valve returns, the pressurized oil
in the drain chamber (D) flows through fine control hole (f')
in the valve on the side that is not operated. The oil passes
through the port (P2), and it flows to the port (B) to replen-
ish the port with pressurized oil.
When the lever is stroked to the end
1.
The lever (5) pushes down the piston (4), and the retainer
(9) pushes down the spool (1).
2.
The fine control hole (f) is disconnected from the drain
chamber (D) and connected to the pump pressure cham-
ber (PP).
3.
The pilot pressure oil from the self-pressure reducing valve
flows to port (A) through fine control hole (f) and port (P1),
and it pushes the control valve spool.
4.
The oil returning from the port (B) flows from port (P2)
through the fine control hole (f') to the drain chamber (D).
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10 STRUCTURE AND FUNCTION
PC500LC-10R