Various types of flap doors

A flap gate is a one-way valve device installed at the end of drainage pipelines to prevent backflow of external water, primarily relying on the pressure difference of the medium to achieve automatic opening and closing.
Structure and Working Principle
It consists of four parts: valve seat, valve plate, sealing ring, and hinge, available in both circular and square shapes. When the water pressure inside the pipeline exceeds the external pressure, it automatically opens for drainage. If the external pressure increases, the valve plate closes under its own weight without manual operation.
Materials and Classification
Traditional Materials: Mainly stainless steel, cast iron, and structural steel.
New Composite Materials: Such as fiberglass reinforced plastic (FRP) and high-density polyethylene (HDPE), which are lightweight, corrosion-resistant, and feature rapid opening. These represent the future development trend.
Applicable Scenarios
Widely used in water conservancy systems, municipal sewage systems, flood control and drainage, sewage treatment plants, and other settings. It is particularly suitable for preventing backflow when the tidal level of rivers is higher than the pipeline outlet.