Specifies requirements for the design, manufacture and testing of closed expansion vessels with built in diaphragm, which will hereinafter be called "vessels", and a) whose diaphragm serves to separate water on the one hand and air / nitrogen on the other hand in heating/cooling systems or fresh water systems; b) which are manufactured singly or in series; c) which may consist partly or entirely of (cold) deep-drawn parts; d) whose parts may be joined by welding, clenching or flanges; e) whose size is not limited; f) whose maximum allowable pressure is greater than 0,5 bar, yet not exceeding 30 bar; g) whose upper wall thickness is limited to 12 mm for austenitic steels and 15 mm for ferritic steels; h) whose minimum operating temperature is not below - 10 °C, whose maximum operating temperature is not above 70 °C.