Komatsu PC200-8M0 Shop Manual page 207

403 Hydraulic system, Part 3
Swing motor
Relief valve portion
Outline
q The relief valve portion consists of check
valves (2) and (3), shuttle valves (4) and (5),
and relief valve (1).
Function
q When the machine is in the swing holding
mode, control valve (6) closes the motor outlet
circuit, but the motor rotation is continued by
inertial force.
q The motor output, therefore, is abnormally
increased, resulting in damaging the motor.
In order to prevent the motor damages, the
q
relief valve relieves the abnormally high pres-
sure to port (S) from the motor outlet side
(high-pressure side) of the motor.
Operation
1 When starting swing
When the swing control lever is operated to the
q
right- swing, the pressurized oil from the pump is
supplied to port (MA) through control valve (6).
The pressure on port (MA) rises, the starting
q
torque is generated in the motor, and the motor
starts to rotate.
q The pressurized oil from the outlet port of the
motor passes from port (MB) through the con-
trol valve (6) and returns to the tank.
PC200, 200LC, 220, 220LC-8M0
2 When swing is stopped
q When the swing control lever is returned to
neutral, the supply of pressurized oil from the
pump to port (MA) is stopped.
q The pressurized oil from the motor outlet can't
return to the tank since the returning circuit to
the tank is closed from control valve (6). Thus,
pressure on port (MB) increases.
q Rotation resistance is generated on the motor
and hence the brake starts working.
Shuttle valve (4) is pressed as pressure on
q
port (MB) goes above port (MA).
q The pressure on chamber (C) is increased to
the se t pr es sur e of r el ief va lv e ( 1) an d
becomes the same as that of port (MB).
q A high braking torque works on the motor,
thereby stopping the motor.
When relief valve (1) is being actuated, the
q
relieved pressurized oil and the pressurized oil
from port (S) are fed to port (MA) through
check valve (3).
q Above prevents cavitation on port (MA).
SEN06121-00
9
10-403