ISO 16137:2006 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 degrees Celsius and + 120 degrees Celsius, for a lifetime of 25 years, and also specifies their tests.. ISO 16137:2006 is applicable to valves to be installed in industrial pipe systems, irrespective of the field of application and the fluids to be conveyed. It is concerned with the range of DN 8, DN 10, DN 15, DN 20, DN 25, DN 40, DN 50, DN 65, DN 80, DN 100, DN 125, DN 150, DN 200, DN 250, DN 300, DN 350, DN 400, DN 500 and DN 600, and the range of PN 6, PN 10, PN 16, PN 25, and Class 150 and Class 300.