Glass-reinforced plastic (GRP) gates, also known as composite gates, are primarily composed of unsaturated polyester resin and glass fibers. These gates are a type of one-way valve installed at the outlet of drainage pipes along rivers and canals. When the river or canal water level is higher than the outlet and the pressure exceeds that inside the pipe, the gate panel automatically closes to prevent backflow of river water into the drainage system. 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.