This Standard specifies requirements for the design, construction, testing and performance of thermostatic mixing valves of nominal sizes not larger than DN 32, for use with hot water at a supply temperature not exceeding 90C, and hot and cold water with continuous working pressures not exceeding 1400 kPa. The principal element of the testing procedures is that the thermostatic mixing valve under test does not permit the discharge of water from the outlet with a temperature more than 2C in excess of the nominated discharge temperature. Discharges of water with a temperature in excess of this but which comply with the cumulative time/temperature factors given in Table 4.1 are acceptable.NOTE: Manufacturers may negotiate with the certifying body on hot water supply temperatures up to 99C, or hot and cold water continuous working pressures greater than 1400 kPa or both, if considered desirable, to assess temperature stability of the mixed water (see Clauses 1.7 and 5.2).