Importance

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Abstract

A hypodermic syringe comprises a cylindrical piston barrel, a piston plunger slidable in and extending out one end of the piston barrel, a rubber-like piston attached to one end of the piston plunger, a needle extending from the other end of the piston barrel, and a spring-loaded needle cover in the form of a cover tube slidable over the piston barrel. The cover tube includes a locking mechanism for locking the cover tube in an extended position over the needle or in a retracted position exposing the needle. The locking mechanism comprises an axial slot or keyway provided on the cover tube and having transverse projections at each end, a pin on the piston barrel adjacent to the needle end extending radially outwardly into the slot of the cover tube, and a spring positioned between the distal ends of the piston barrel and the cover tube. In the retracted position of the cover tube, the spring located inside the cover tube is compressed. When an injection is given, the cover tube is automatically unlocked and the compressed spring expands, pushing the cover tube over the needle. Once over the needle, the cover tube is locked in place. In operation the slot rides against the pin and guides the movement of the cover tube.

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First Claim