Waterman Flap gates are installed at the end of pipe lines to allow free outflow and prevent backflow. Waterman Flap Gates can be made of either Stainless steel (304L or 316L) or Aluminum to provide a corrosion-resistant rust-proof automatic drainage and backflow prevention system. With J-bulb neoprene adjustable seats, they assure excellent sealing against return flow. Waterman provides various shapes of flap gates depending on the shape of the opening. (round, rectangular or square openings). Flap gates can be designed flat back for wall mounted applications or flange back to mate with a pipe flange. Size ranges from 12″ to 72″ pipe diameters.