Cast iron shot round shoot the door is the door of the most widely used, mainly installed in the end of the drain pipes to prevent external water intrusion. Material into ordinary gray cast iron, malleable iron, ductile iron and other materials. Cast iron round shot door is a one-way valve installed in the river river drainage outlet, when the river tide is higher than the outlet port, and the pressure is greater than the pressure inside the pipe, cast iron round shot door panel automatically shut down to prevent intrusion into the tidal rivers drains inside.