Komatsu PC88MR-10 Shop Manual page 134

10 Structure and function
Main pump
Operation
(PC88MR-C2B0-044-K-00-A)
Action of spring
The spring force of spring (2) in the PC valve is determined by the angle of the swash plate.
When servo piston (6) moves to the right, spring (2) is compressed by operation of lever (1) and the load
of the spring changes. The spring has characteristics that the spring constant changes into 2 stages
depending on the height of the spring.
When pump pressure (PAVE) is low
When load is light
Weakening in the pressing force of spool (4) causes spool (3) to lean towards the right side. When port (C)
and (D) are connected, pressure which goes in the LS valve turns into drain pressure (PT)
When port (F) is connected to port (G) of the LS valve, the pressure in port (J) becomes drain pressure
(PT) and servo piston (6) moves to the left.
Pump discharged volume increases.
As servo piston (6) moves, lever (1) moves to the left and spring (2) expands and the spring force is
decreased. Consequently, spool (3) moves to the left and port (C) is disconnected from port (D), and ports
(B) and (C) are connected.
Since the pressure in port (C) rises and the piston pressure is increased, servo piston (6) stops moving to
the left.
10-56 PC88MR-10