② · When stopping swing When the swing control lever is returned to neutral, no pressurized oil is supplied from the pump to port B. The return circuit to the tank is closed by the control valve. So the oil from the outlet port of the motor increases in pressure at port A. Resistance to the rotation of the motor is created, and the brake starts to act. The pressure at port A rises to the set pressure of make up valve a, and in this way, a high brake torque acts on the motor, and the motor stops. When make up valve a is being actuated, the relief oil from make up valve a and the oil from port Mu pass through check valve CB and are supplied to port B.
This prevents cavitation from forming at port B. SH PG · GB · A Mu B 2-16