a protective device for employing in an accumulator wherein , in a pressure vessel , a separating member dividing the interior of the pressure vessel and a supporting cylinder having open pores as said protective device are coaxially arranged in order of approaching the axis . the protective device is for protecting the separating member from damage when the separating member is pressed against the supporting cylinder . by virtue of employing the novel protective device in an accumulator , the fluid flow through the supporting cylinder is not hindered and no fragments detached from the material of supporting cylinder enter the fluid to damage the fluid system .