The working principle of the axial flow check valve: the opening and closing of the valve flap is determined by the pressure difference between the inlet end and the outlet end of the valve. The flap opens when the pressure at the inlet end is greater than the sum of the spring forces at the outlet end. As long as there is a pressure difference, the valve flap is always open, but the degree of opening is determined by the magnitude of the pressure difference. When the sum of the outlet end pressure and the spring force is greater than the inlet end pressure difference, the flap is closed and remains closed. Since the opening and closing of the valve flap is in a dynamic force balance system, the valve is balanced, no noise, and the water hammer phenomenon is greatly reduced.