Non-reusable syringe

Abstract

A syringe tubular body forms a fluid receiving chamber having a restricted opening at one end for receiving a hollow needle and a wider opening at the other end for receiving a tubular plunger. The plunger has resilient fingers at its distal end which is inserted into the body chamber and an annular groove in one embodiment adjacent the proximal end. The fingers have inwardly extending hook-like projections. A piston assembly includes a body with an annular groove which releasably receives the projections for securing the piston assembly to the plunger during injection, the piston assembly including an elastomeric disc piston sealingly engaged with the tubular body chamber sides. A sleeve is external and movable along the body and is next adjacent the disc. The sleeve has an annular groove which is selectively engaged by the projections. The sleeve has an axial extent greater than that of the piston assembly body groove. When the piston is fully inserted into the chamber during injection, further displacement forces the disc piston against the chamber bottom permitting the finger projections to be forced out of engagement with the piston assembly body groove and into locking engagement with the sleeve groove, or in the alternative, to break away. When the plunger is withdrawn from the chamber, the engaged sleeve is withdrawn therewith and precludes the projections from engaging the piston assembly body groove leaving the piston in the chamber to preclude further use of the syringe tubular body. When the projections break, the piston is also left in the body chamber.