This document specifies: a) field of application; b) requirements for hose union backflow preventer; c) dimensional and the physico-chemical properties and the properties of general hydraulic, mechanical and acoustic design of hose union backflow preventers DN 15 to DN 32; d) test method and requirements for verifying these properties; e) marking and the presentation; f) acoustics. This document specifies the characteristics of hose union backflow preventers DN 15 to DN 32 that are suitable for use in drinking water systems at pressures up to 1 MPa (10 bar) and temperatures up to 65 celcius degrees and for 1 h at 90 celcius degrees.