This European Standard specifies dimensions, materials and performance requirements (including methods of test) for hydraulic safety groups, of nominal sizes from DN 15 to DN 25, having working pressures1) from 0,1 MPa (1 bar) to 0,7 MPa (7 bar). Hydraulic safety groups are intended for fitting to the portable water supply of storage water heaters, having a maximum storage temperature of 95°C. Hydraulic safety groups limit the pressure in hot water heaters, prevent the backflow of water into the main circuit and prevent the discharged water to get into contact with the water in the water heater. Hydraulic safety groups do not control the temperature. They ascertain the hydraulic safety of water heaters if the mechanical resistance of the water heater remains at least equal to the rating pressure. NOTE The use of the device specified in this Standard does not override the need to use controls (e. g. thermostats and cut-outs) which act directly on the power sources of water heaters.