Syringe with automatic retracting needle

Claim 1

In a syringe for administering injections to a patient, said syringe including a hollow tubular member defining a chamber for storing fluids to be injected, a hypodermic needle connected to a discharge end of said tubular member, and a hollow plunger reciprocally movable between up and down positions in said tubular member, the improvement wherein said needle is fastened to a needle retraction block, lock means fixedly connected to said tubular member within said chamber for securing said block and needle in a first orientation with the needle protruding outwardly of said tubular member, and retraction means carried by said plunger for mating with said block and for disengaging said lock means as the plunger is reciprocated into said full down position, and biasing means located within said plunger and operatively connected to said retraction means, said biasing means for automatically retracting said needle into said plunger when the plunger reaches its full down position, said retraction means includes a shaft which is press-fitted into said plunger, said shaft including a lower protrusion matable with said block for allowing one-way movement of the block, said biasing means includes a spring operatively connected to said shaft within said plunger, said shaft includes a foot part radially spaced from said protrusion, and said lock means includes an inwardly protruding flexible lip bearing on said block, said foot part contacting and bending said lip away from said block when the plunger is in said full down position whereby said lock means is disengaged and flexes the foot inward which removes contact between the plunger and the shaft thus allowing the needle to be retracted.