In systems using this type of motor, without a balancing function valve, it will happen that the speed exceeds the hydraulic oil supply to the motor. In order to prevent cavitation caused by insufficient oil supply, a special oil filling valve is installed to compensate for insufficient oil supply. A charge valve is installed in front of the oil port to the hydraulic oil tank, which ensures the supply pressure required by the hydraulic motor to perform the function of the hydraulic pump. The increased pressure is applied to the oil supply port of the hydraulic motor through the oil charge valve. Oil pressure enters port B and the motor reverses. If the plunger of the main control valve moves to the middle position, the oil in the motor flows out through the left overflow valve, and the outflow oil flows into the motor through the right charge valve, thereby preventing the motor from cavitation.