Komatsu PC88MR-10 Shop Manual page 212

10 Structure and function
Work equipment and swing PPC valve
When valve is in fine control range
(neutral to fine control range)
When piston (4) is pushed by disc (5), retainer (9) is pushed and spool (1) is also pushed by metering
spring (2) and moves downward.
Almost at the same time when fine control hole (f) is disconnected from drain chamber (D), it is connected
to pump pressure chamber (PP).
The pilot pressure oil of main pump is transmitted from port (P1) to port (A) through fine control hole (f).
When the pressure in port (P1) becomes higher, spool (1) is pushed back and fine control hole (f) is
disconnected from pump pressure chamber (PP). At almost the same time, it is connected to drain
chamber (D) to release the pressure in port (P1).
Spool (1) moves up and down to balance the force of metering spring (2) with the pressure in port (P1).
The positional relationship between spool (1) and valve body (10) [fine control hole (f) is located between
drain chamber (D) and pump pressure chamber (PP)] does not change until retainer (9) comes in contact
with spool (1).
Metering spring (2) is compressed in proportion to the stroke of the control lever.
The pressure in port (P1) also increases in proportion to the stroke of the control lever.
Accordingly, the control valve spool moves to a position at which the pressure in chamber (A) [equal to the
pressure in port (P1)] is balanced with the reaction force of the return spring of the control valve spool.
10-134 PC88MR-10