Komatsu Galeo BR380JG-1E0 Shop Manual page 157

SEN01353-00
2) Safety valve
Function
As long as the machine travel is stopped (or it
q
is travelling downhill), the counterbalance
valve closes the inlet and outlet circuits of the
motor.
Since the motor is rotated by inertial force,
q
pressure in the motor outlet port side is abnor-
mally increased, potentially resulting in dam-
ages on the motor and piping.
The safety valve releases this abnormal pres-
q
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) (Clockwise rotation)
Reduction of the pressure at motor inlet (PA)
q
decreases the pressure in chamber (S1).
When it drops beyond the spool switching
q
pressure, spool (19) is returned to the left by
spring (20), reducing the pressure at outlet
passage (B1).
The motor tries to continue rotation resorting to
q
inertial force, thus pressure on the outlet port
(MB) is increased.
14
10 Structure, function and maintenance standard
When the pressure rises above the set pressure
q
of the suction safety valve, poppet (1) opens.
The pressurized oil passes through notch (A1)
q
of spool (19) into chamber (MA) of the circuit at
the opposite side.
At the time of counterclockwise rotation, it
q
makes reverse operation of clockwise rotation.
3) When starting travel
(or when traveling at a constant speed)
As the travel lever is operated, the pressurized
q
oil from the pump moves spool (19) toward right.
The passage to the suction safety valve func-
q
tions as a circuit which passes through notch
(B2) of spool (19), producing large differential
pressure.
The pump pressure rises, providing a large
q
tractional force to the valve.
BR380JG-1E0