Komatsu PC200-8M0, Shop Manual

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SEN06121-00
PC200, 200LC, 220, 220LC-8M0 10-403
31
403 Hydraulic system, Part 3
PPC valve
3) During fine control
(When control lever is returned)
q
When lever (5) starts to be returned, spool (1)
is pushed up by the force of centering spring
(3) and pressure at port (P1).
q
Because of this, fine control hole (f) is con-
nected to drain chamber (D), and the pressur-
ized oil at port (P1) is released.
q
If the pressure of port (P1) is lowered exces-
sively, spool (1) is pushed down by metering
spring (2).
q
Fine control hole (f) is shut off from drain cham-
ber (D), and it is almost simultaneously inter-
connected to pump pressure chamber (PP).
q
Pump pressure is supplied until the pressure at
port (P1) recovers to the level equivalent to the
lever position.
q
When the spool of the control valve returns,
the oil in drain chamber (D) flows in from fine
control hole (f') in the valve on the side that is
not working. The oil passes through port (P2)
and enters chamber (B) to replenish the cham-
ber with pressurized oil.
4) At full stroke
q Lever (5) pushes down piston (4), and retainer
(9) pushes down spool (1).
q Fine control hole (f) is shut off from drain
chamber (D), and is interconnected to pump
pressure chamber (PP).
q Therefore, the pilot pressure oil from the self
pressure reducing valve passes through fine
control hole (f) and flows to chamber (A) from
port (P1) to push the control valve spool.
q The oil returning from chamber (B) passes
from port (P2) through fine control hole (f') and
flows to drain chamber (D).