Komatsu PC200-8M0 Shop Manual page 228

SEN06121-00
1. Pressure reducing valve function
Operation
1) When in neutral
q 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)
q When piston (4) is pushed by lever (5), retainer
(9) is pushed, spool (1) is also pushed by
metering spring (2), and moves down.
q When fine control hole (f) is shut off from drain
chamber (D), it is almost simultaneously inter-
connected to pump pressure chamber (PP).
q Pilot pressurized oil of the control pump is led
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).
q As a result, spool (1) moves up and down until
the force of metering spool (2) is balanced with
the pressure at port (P1).
30
10-403
403 Hydraulic system, Part 3
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).
q Metering spring (2) contracts in proportion to
the stroke of the control lever.
q Pressure at port (P1) also rises in proportion to
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.
PC200, 200LC, 220, 220LC-8M0
PPC valve