Pressure tank, in particular hydraulic accumulator

A pressure tank, comprising:

• a housing having a first space for receiving a first working medium and a second space for receiving a second working medium;
• and
• a resilient separating element being a rolling membrane and movable with deformation thereof, separating said first space and said second space in said housing and defining a generally hemispherically domed main separating surface extending from an annular edge to a bottom end, said separating element being formed of a substance having a fluoroplastic material;
• and
• annular bead shaped elevations on said separating element projecting inwardly from said domed main separating surface, said elevations being folds having open ends on an outer side of said domed main separating surface and forming annular groove-shaped depressions on said outer side of said domed main separating surface, said folds having vertical axes extending from said open ends thereof to peaks thereof, said vertical axes of adjacent ones of said folds being tilted at increasingly greater angles to a plane containing said annular edge from said annular edge to said bottom end.