Komatsu PC200-8M0, Shop Manual, Page: 219 / 1254

SEN06121-00
PC200, 200LC, 220, 220LC-8M0 10-403
21
403 Hydraulic system, Part 3
Travel motor
2) Safety valve
Function
q As long as the machine travel is stopped (or it
is travelling downhill), the counterbalance
valve closes the inlet and outlet circuits of the
motor.
q Since the motor is rotated by inertial force,
pressure in the motor outlet port side is abnor-
mally increased, potentially resulting in dam-
ages on the motor and piping.
q The safety valve releases this abnormal pres-
sure to the inlet port side of the motor in order
to prevent damages to the equipment.
Operation
(1) When travel is stopped
(or when travelling downhill) (Right swing)
q Reduction of the pressure at motor inlet (PA)
decreases the pressure in chamber (S1).
q When it drops beyond the spool switching
pressure, spool (19) is returned to the left by
spring (20), reducing the pressure at outlet
passage (B1).
q The motor tries to continue rotation resorting to
inertial force, thus pressure on the outlet port
(MB) is increased.
q
When the pressure rises above the set pressure
of the suction safety valve, poppet (1) opens.
q
The pressurized oil passes through notch (A1)
of spool (19) into chamber (MA) of the circuit at
the opposite side.
q At the time of counterclockwise rotation, it
makes reverse operation of clockwise rotation.
(2) When starting travel
(or when traveling at a constant speed)
q
As the travel lever is operated, the pressurized
oil from the pump moves spool (19) toward right.
q
The passage to the suction safety valve func-
tions as a circuit which passes through notch
(B2) of spool (19), producing large differential
pressure.
q
The pump pressure rises, providing a large
tractional force to the valve.