A pressure tank, in particular hydraulic accumulator (3, 5), has a parting element (1) separating a space (11) for a first gaseous working medium from a space for a second fluid working medium in the tank. The parting element is flexible, can move under deformation and defines a domed main parting plane extending from an annular edge (13). The parting element (1) is produced from a substance having a fluoroplastic material, preferably a substance composed entirely of fluoroplastic material.