Komatsu PC500LC-10R Shop Manual page 302

COMPONENT PARTS OF WORK EQUIPMENT SYSTEM
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 the disc (5) starts
being 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 disc (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).
1ST-LINE ATTACHMENT PPC VALVE (WITH EPC VALVE)
PPC
Abbreviation for Proportional Pressure Control
EPC
Abbreviation for Electromagnetic Proportional Control
STRUCTURE OF 1ST-LINE ATTACHMENT PPC VALVE (WITH EPC VALVE)
(Machines ready for installation of attachment)
10-208
10 STRUCTURE AND FUNCTION
PC500LC-10R