The residual pressure valve has good adaptability to the sudden static pressure change. Generally, it should be set on the outer wall of the leeward side between the clean rooms with different static pressure differences, and should not be located in the indoor airflow place that obviously affects the downstream side. The modified device consists of a frame, a valve plate and a counterweight. The maximum opening angle of the valve plate is 45°. It can be widely used in the purification workshop or clean room to maintain the positive pressure difference between the indoor and outdoor, so that the excess air in the room is discharged and prevented. Outdoor air intrusion.