This document specifies: a) the field of application; b) the requirements of hose union anti vacuum valves; c) dimensional and physio-chemical properties, and properties of general hydraulic, mechanical and acoustic design of hose union anti-vacuum valves of nominal sizes DN 15 up to and including DN 25; d) marking and technical product information. This document specifies the characteristics of hose union anti-vacuum valves of nominal size DN 15 up to and including DN 25 that are suitable for use in drinking water systems at pressures up to and including 1 MPa (10 bar) and temperatures up to and including 65 °C and for 1 h at 90 °C. HB protects against back siphonage only and is installed in vertical downward flow position. HB and HD anti-vacuum valves are for installation exclusively at the connecting point between stop valve and hose in vertical downward flow position.