Hyundai Excavator R450LC-7. Service and repair manual - page 11

3-20

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 pressure at the shuttle valve is
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.

1)

2)

3)

4)

45073HC15-1

3-22

TRAVEL CIRCUIT OPERATION

TRACK MOTOR DEVICE

A

B

COUNTER BALANCE VALVE

TURNING JOINT

TO/FROM CONTROL VALVE

A

B

PK

OVERLOAD RELIEF VALVE

CHECK VALVE

Valves are provided on travel motors to offer the following functions.

CHECK VALVE
Stopping the motor, this valve sucks the oil from lower pressure passage for prevention the negative
pressure and the cavitation of the motor.

COUNTER BALANCE VALVE
When stopping the motor of slope descending, this valve to prevent the motor over run. 

OVERLOAD RELIEF VALVE
Relief valve limit the circuit pressure below 345kgf/cm

2

to prevent high pressure generated at a time

of stopping the machine.  Stopping the motor, this valve sucks the oil from lower pressure passage
for preventing the negative pressure and the cavitation of the motor.

1)

2)

3)

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