Komatsu Galeo PC138US-8 Shop Manual page 205

10 Structure, function and maintenance standard
Relief valve portion
Outline
The relief valve portion consists of check
q
valves (2) and (3), shuttle valves (4) and (5),
and relief valve (1).
Function
When the machine is in the swing holding
q
mode, control valve (6) closes the motor outlet
circuit, but the motor rotation is continued by
inertial force.
The motor output, therefore, is abnormally
q
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) via control valve (6).
The pressure on port (MA) rises, the starting
q
torque is generated in the motor, and the motor
starts to rotate.
The pressurized oil from the outlet port of the
q
motor passes from port (MB) through the con-
trol valve (6) and returns to the tank.
PC138US, USLC-8
2. When swing is stopped
When the swing control lever is returned to
q
neutral, the supply of pressurized oil from the
pump to port (MA) is stopped.
The pressurized oil from the motor outlet can't
q
return to the tank since the returning circuit to
the tank is closed from control valve (6). Thus,
pressure on port (MB) increases.
Rotation resistance is generated on the motor
q
and hence the brake starts working.
Shuttle valve (4) is pressed as pressure on
q
port (MB) goes above port (MA).
The pressure on chamber (C) is increased to
q
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).
A high braking torque works on the motor,
q
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) via check
valve (3).
Above prevents cavitation on port (MA).
q
SEN02550-01
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