A gas spring accumulator comprising:—a housing (2, 3) provided with an inlet (20); and—a flexible diaphragm (4) dividing the interior of the housing into a working chamber (7) which is exposed to system pressure via the inlet, and a gas chamber (6); characterised in that the housing includes a diaphragm element (4) having one side exposed to system pressure via the inlet (20) and an opposite side exposed to a further chamber (13), a first non-return valve (17) arranged to admit atmospheric gas into the further chamber (13), and a second non-return valve (29) arranged to admit gas from the further chamber (13) into the gas chamber (6).