SWING CIRCUIT OPERATION SWING MOTOR DEVICE BRAKE RELEASE VALVE BRAKE OFF PG DB BRAKE ON M MAKE UP VALVE MOTOR BRAKE VALVE PA ANTI-REACTION VALVE MAKE UP PORT(M) A(CW) B(CCW) TO / FROM MAIN CONTROL VALVE 900L3HC17 1) MOTOR BRAKE VALVE Motor brake valve for the swing motor limits to cushion the starting and stopping pressure of swing operation and controls the swing motor operating pressure. 2) MAKE UP VALVE The make up valves prevent cavitation by supplying return oil to the vacuum side of the motor. 3) PARKING BRAKE This is function as a parking brake only when all of the RCV lever (except travel pedal) are not operated.
PARKING BRAKE "OFF" OPERATION The parking brake is released by the pilot pressure oil from the pilot pump. When one of the RCV lever (except travel lever) placed in the operating 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 oil pressure PG lift the brake piston and release the parking brake. PARKING BRAKE "ON" OPERATION When all of the RCV 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". 4) ANTI-REACTION VALVE This anti-reaction valve absorbs shocks produced as motion stop and reduced oscillation cause by swing motion. 3-19