This International Standard specifies requirements for the design, functional characteristics and manufacture of check valves made of thermoplastics materials intended to allow the flow of liquid fluids through the valve in one direction only and to prevent backflow, their connection to the pipe system, the body materials and their pressure/temperature rating between − 40 °C and + 120 °C, for a lifetime of 25 years, and also specifies their tests. This International Standard is applicable to valves to be installed in industrial pipe systems, irrespective of the field of application and the fluids to be conveyed.