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's tidal level is higher than the outlet of the pipe and the pressure is greater than the internal pipe pressure, the valve plate closes automatically to prevent the river's tide from backflowing into the drainage pipe. 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 one-way water flow.