Komatsu ecot3 PC300LC-8 Shop Manual page 239

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.
q The motor output, therefore, is abnormally
increased, resulting in damaging the motor.
q In order to prevent the motor damages, the
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
q When the swing control lever is operated to the
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.
PC300, 350-8
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 set pres sure of relief valve (1) and
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) via check
valve (3).
Above prevents cavitation on port (MA).
q
SEN01995-01
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