SWING CIRCUIT OPERATION SWING MOTOR DEVICE PARKING BRAKE SH BRAKE OFF PG BRAKE ON Au ANTI-INVERSION VALVE MOTOR BRAKE VALVE GB MAKE UP VALVE A(CCW) B(CW) MAKE UP PORT(Mu) TO / FROM MAIN CONTROL VALVE 21073HS15A 1) MOTOR BRAKE VALVE Motor brake valve for the swing motor limits to cushion the starting and stopping pressure of swing operation. 2) MAKE UP VALVE The make up valves prevent cavitation by supplying return oil to the vacuum side of the motor. 3) 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".
BYPASS VALVE This bypass valve absorbs shocks produced as swing motion stops and reduced oscillation cause by swing motion. 3-19