The present invention discloses a pressure fluid accumulator with a housing having its interior subdivided into two chambers by a media-separating element, the first chamber being filled with a gas and the second chamber being filled with a liquid, and wherein in a hydraulic port a bottom valve is provided whose closure member is operable by the media-separating element and which permits filling the second chamber with liquid and prevents complete evacuation of the second chamber. In order to prevent a damage of the bottom valve and an inadvertent escape of fluid and, thus, ensure a considerable increase in the reliability in operation, according to the present invention, the closure member can be moved by the media-separating element to adopt a position in which it fulfils the function of a hydraulic piston.