To stabilize a control characteristic in a short time and reduce dispersion of the time up to stability by forming nearly continued projecting parts in the circumferential direction in the vicinity of the outer edges of openings on the outflow sides of a piston, and enabling the outer circumferential parts of valves to be contacted with the projecting parts.
At descent of a rod 1, oil under a piston 3 is compressed, the oil flows from an opening 31 of narrow width, through a flow passage 29, pushes up an upper side valve 5 closing an opening of wide width, and moves over the piston 3. In opposition, at ascent of the rod 1, oil over the piston 3 is compressed, the oil flows in from the opening 31 of narrow width, through the flow passage 29, pushes up a lower side valve 7 closing the opening of wide width, and moves under the piston 3. In this way, the valves 5, 7 repeat contact and separation against the projecting parts 35 of the piston 3. Hereby, the sharp extreme end of the projecting part 35 is worn down to conform, and hence the passing quantity of oil is controlled and the impact is absorbed.
MASUYAMA AKIHIRO
TSUNODA MITSUAKI
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