Restricted use hypodermic syringe

Claim 1

A restricted use hypodermic syringe comprising: a tubular barrel having a forward end, a rearward end and an inner wall surface defining an interior space for accommodating a liquid to be administered and a movable plunger assembly, said barrel having means at said forward end thereof for coupling to a hypodermic needle; a movable plunger assembly received within said barrel, said plunger assembly having (1) a piston with an exterior surface sealingly engaging said inner wall surface of said barrel, (2) a plunger rod having a forward end joined to said piston and a rearward end extending through said rearward end of said barrel and (3) a thin-walled tubular plunger lock disposed within said barrel and surrounding said plunger rod; said plunger lock having inwardly struck rearwardly angled elements engaging said plunger rod to form a one-way clutch which permits movement of said piston and plunger rod relative to said plunger lock in a rearward direction and couples said piston and plunger rod and said plunger lock for movement together in a forward direction; said plunger lock having outwardly struck rearwardly angled elements engaging said inner wall of said barrel to form a one-way brake which permits movement of said plunger lock in said barrel in a forward direction and prevents movement of the plunger lock in a rearward direction; whereby (1) the piston and plunger rod can be moved rearwardly in said barrel from a first position to a second position for drawing liquid into said barrel, (2) subsequently said piston and plunger rod and said plunger lock can be moved together in said barrel forwardly from said second position to a third position to expel liquid from said interior space and establish a blocking position of said plunger lock and (3) thereafter the extent of rearward movement of said piston and plunger rod in said barrel is limited by the blocking position of said plunger lock.