The axial flow check valve is a device that determines the valve flap switch by the pressure difference between the inlet and outlet ends of the valve. When the pressure at the inlet and outlet cycles is the sum of the spring forces, the valve flap will automatically open. And vice versa. In summary, as long as there is a pressure difference, the valve flap will remain open. Keep in mind that in axial flow check valves, the pressure difference is the most important factor in keeping the valve closed. You must protect the valve disc and the spring to ensure a long life.