Hyundai Excavator R450LC-7. Service and repair manual - page 12

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SWING CIRCUIT OPERATION

MOTOR BRAKE VALVE
Motor brake valve for the swing motor limits to cushion the starting and stopping pressure of swing
operation.

MAKE UP VALVE
The make up valves prevent cavitation by supplying return oil to the vacuum side of the motor.

PARKING BRAKE
In case that the parking, of the machine at slope is required during operation, there is the danger of
involuntary swing caused by the self weight of the machine.   The brake is connected to prevent this
involuntary swing.

PARKING BRAKE "OFF" OPERATION
The parking brake is released by the pilot pressure oil from the pilot pump.
When the left control lever placed in the swing position, the pilot oil flows into SH port through the
MCV. This pressure transferred to the brake release valve and the brake release valve is change
over.   Then the pilot pressure lift the brake piston and release the parking brake.

PARKING BRAKE "ON" OPERATION
When the control lever placed in the neutral position, the pressure of the pilot oil passage down.
Then the brake release valve returned to the neutral position and the oil is returned from the brake
piston to the tank.   And the brake is set to 'ON".

REACTIONLESS VALVE
This bypass valve absorbs shocks produced as swing motion stops and reduced oscillation cause
by swing motion.

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45073HC15-1