The flap valve is composed of valve body, valve flap, hinge and copper alloy sealing surface. This series of flap door has two shapes, round and square, both of which are connected by double hinges of valve body and valve flap to ensure safe and reliable connection. This product has a simple structure and does not require manual operation. Flanges or embedded connections can be used for connection. Sealing can be realized by reverse bearing water head of 8m. It is suitable for irrigation, waterworks, flood prevention, sewage treatment and other industries, and can eliminate the effect of water flow back irrigation.