Improvements in or relating to hypodermic syringes

摘要

A disposable hypodermic syringe, which is provided with the needle fitted and sheathed, provides automatic retraction of the needle after use. The syringe may be supplied pre-charged with an injectant. The completion of the injection stroke attaches the piston to the needle carrier and subsequently dislodges a retaining ring thereby freeing the piston from the plunger and releasing stored energy of a spring or the like to draw the piston and needle carrier into the plunger. The plunger is positively retained inside the housing by the interaction of rings. Alternative methods of locating the needle carrier during use and of attaching the piston to the needle carrier to enable retraction are shown. An alternative method of retaining the piston on the plunger is also shown. A further configuration is shown affording the use of an offset needle. The syringe has optional features to prevent unwanted inward movement of the plunger and to prevent seepage of liquid after use.