| 摘要 |
A tamper proof retractable non-reusable syringe has a one-piece hollow outer body (12) with a barrel (14) for a slidable plunger (32), a transition zone, and a smaller diameter nose portion (16). An elongated needle holder (22) and spring combination is installed from the rear of the outer body, guided into the nose portion and held by cooperating inwardly and outwardly facing surfaces oriented in the direction of retraction at the most constricted part of the transition zone where the nose begins. The plunger has an opening (41) with a dislodged stopper (42) for receiving parts of the retraction mechanism. The stopper and the head of the needle holder are of significantly reduced diameter from the injection fluid chamber to resist blowing out prematurely. In one embodiment the head of the needle holder is surrounded by a separable retainer member which is sliding removed by contact with the tip of the plunger after the stopper is mostly or fully removed to avoid cumulation of force required for retraction after the injection. In a second embodiment the head of the needle holder is clamped, and held by constricting forces imposed by stress on the outer body induced by interference fit. Release occurs by slight expansion on the barrel by contact of the plunger tip with a small internal ramp in the outer barrel. Both embodiments have a plunger cap configured to enter an opening in the outer body to provide an additional tamper proof feature. The retraction cavity is provided with venting structures to assure that all uninjected fluid is retained within the syringe body.
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