Komatsu PC200-8M0, Shop Manual

Page: 133 / 1254

SEN06119-00
PC200, 200LC, 220, 220LC-8M0 10-401
21
401 Hydraulic system, Part 1
Hydraulic pump
(2) When load on actuator is large and pump discharge pressure is high
Outline
q When the load is large and pump discharge
pressures (PP1) and (PP2) are high, the force
pushing spool (3) to the right becomes larger
and spool (3) will be moved to the position
shown in above figure.
q Part of the pressure to be conducted from port
(C) to LS valve flows from port (B) to port (C)
and (D) through LS valve. At the end of this
flow, level of this pressure becomes approxi-
mately half of the main pump pressure (PP2).
Operation
q
When port (E) and port (G) of the LS valve are
connected, this pressure from port (J) enters
the large diameter end of servo piston (9),
stopping servo piston (9).
q
If main pump pressure (PP2) increases further
and spool (3) moves further to the right, main
pump pressure (PP1) flows to port (C) and acts
to make the pump discharge the minimum.
q
When servo piston (9) moves to the right,
springs (4) and (6) are compressed and push
back spool (3).
q
When spool (3) moves to the left, the opening
of port (C) and port (D) becomes larger.
q
As a result, the pressure on port (C) (= J) is
decreased and the rightward move servo pis-
ton (9) is stopped.
q
The position in which servo piston (9) stops at
this time is further to the right than the position
when pump pressures (PP1) and (PP2) are
low.
q
The relationship between the average pump
pressure (PP1 + PP2)/2 and servo piston (9) in
terms of their positions can be represented by
the broken line in the figure springs (4) and (6)
form the double springs.