A diaphragm pressure expansion vessel (1) which is intended to be connected to a line system having two vessel parts (2, 3) which are connected to one another in a pressure-tight and fluid-tight manner in a peripheral connecting region (4), wherein the closed vessel interior (10) which is formed by the two vessel parts (2, 3) is separated into a water chamber (6) and a gas chamber by a diaphragm (5), wherein the water chamber (6) can be connected to the line system via a connection piece (7), wherein the diaphragm (5) is formed from an at least single-layered plastic and is in the form of a bubble, should be developed further such that the risk of fracture of the plastic diaphragm when subjected to loading during replacement is considerably reduced. This is achieved in that the gas chamber is formed by the diaphragm interior (9) and by the vessel interior (10) between that side of the diaphragm (5) which is averted from the water chamber (6) and the adjoining vessel part, wherein that side of the diaphragm (5) which is averted from the water chamber (6) is provided with perforations.