A hydraulic accumulator includes a rigid tank containing a flexible but non-elastic bladder formed of a metal foil and separating the interior of the tank into a gas space and a liquid space. The gas and liquid spaces respectively communicate with exterior sources of gas and liquid through fixtures provided on the accumulator tank. One of the fixtures is provided with an anti-extrusion valve to prevent the bladder from being forced out through the fixture. In one preferred embodiment the bladder is a bellows. In another preferred embodiment the accumulator tank is provided with a vent in communication with the liquid space within the tank to allow for venting of any gas separating from the liquid and accumulating within the liquid space.