Glass-fiber reinforced plastic (GFRP) butterfly valves, also known as composite butterfly valves, are primarily composed of unsaturated polyester resin and glass fibers. These valves are a type of one-way valve installed at the outlet of drainage pipes along rivers. When the river level is higher than the outlet of the pipe and the pressure exceeds the internal pressure, the butterfly valve panel automatically closes to prevent river water from backflowing into the drainage pipeline. They are suitable for overflow and backflow prevention in various pipelines and water channels for water supply, drainage, and wastewater treatment projects, and are used at outlets for unidirectional water flow.