a hollow membrane that is both rigid and flexible the membrane itself can absorb pressure and or a water volume increase this is in contrast to the conventional use a diaphragm provided with an air precharge because in such diaphragm systems it is the air precharge that provides the absorption of pressure and or water volume increase by compressing the air in a fixed volume according to another embodiment of the present invention e g as shown in the embodiment in fig4 b and 5 a hollow membrane 12 is provided that contains within the membrane itself a precharged air cushion to absorb a pressure shock in such an embodiment the precharged air cushion primarily provides the membrane 12 with the resistance to the pressure shock and or water volume increase as shown in fig4 b and 5 this embodiment containing the air precharge generally has a thinner and more flexible membrane compared with the embodiment that does not contain an air precharge as shown in fig3 a 3b the housing 14 can be of a shape similar to that of the membrane 12 housed thereon of course the housing 14 shape is not limited to shapes corresponding to that of the membrane contained therein provided that it can adequately house the membrane 12 and allow the membrane 12 to come into contact with fluid forced inside of the housing 14 as the result of a pressure shock and or water volume increase and flex and compress as a result of such contact preferably the housing 14 is sized and shaped such that there is not excessive space surrounding the membrane 12 which.