Komatsu ecot3 PC300LC-8 Shop Manual page 232

SEN01995-01
2. Safety valve
(bidirectional 2-stage set 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.
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.
Bidirectional action
1) When pressure in chamber (MB) has
become high (when rotating clockwise)
q As long as the machine travel is stopped (or it
is travelling downhill), the check valve of coun-
terbalance valve closes chamber (MB) of the
outlet port circuit.
q The motor tries to continue rotation resorting to
inertial force, thus pressure on the outlet port
(MB) is increased.
40
10 Structure, function and maintenance standard
As the pressure goes above the set pressure,
q
[Difference in areas of circles (D1) and (D2) x
Pressure] compresses spring (2).
q Poppet (1) is moved leftward and the pressur-
ized oil flows into chamber (MA) of the oppo-
site circuit.
PC300, 350-8