Backflow preventer is mainly used to prevent the medium in the pipeline from backflow due to pressure inversion, applicable to water, air and non-corrosive liquids, widely used in municipal water supply, building water supply and drainage, fire-fighting and industrial circulation system. Working temperature is generally 0 ℃ to 80 ℃, special materials can withstand higher temperatures. It is suitable for normal pressure to low and medium pressure working conditions. The main function is to realize double protection through the internal non-return and pressure relief structure to prevent backflow of contaminated media. Commonly used materials include copper alloy, stainless steel and ductile iron, compact structure, easy maintenance, to protect the system water quality safety and operational stability.