Self-aspirating syringe with positively engaged locking collet

Claim 1

A self-aspirating hypodermic syringe of the type used in combination with a cartridge ampoule which is sealed at its upper end by a slidable piston and at its lower end by a pierceable membrane, and which contains an injectable fluid therein, which comprises a syringe holder having: (A) a head; (B) a barrel attached thereto for receiving said cartridge ampoule and provided at its lower end with a double ended needle for communication with the cartridge ampoule contents; and (C) a generally cylindrical holding means within said head, said holding means being adapted for: (1) securely holding said cartridge ampoule within said barrel; (2) receiving within the bore thereof a double plunger mechanism comprising an inner plunger slidable within the bore of, and biased against, an outer plunger, said inner plunger having interengagement means for making positive interengagement with the slidable piston closing the upper end of said cartridge ampoule; and (3) positively, selectively and reversibly locking said outer plunger within the head of said syringe holder thereby to immobilize said outer plunger against axial movement relative to said syringe holder, whereby upon alternate exertion of downward pressure upon said inner plunger and release thereof when said holding means is in locking engagement, the bias of said inner plunger against said outer plunger creates aspirating conditions within said ampoule and whereby upon exertion of downward pressure upon said inner plunger when said holding means is unlocked, said inner and outer plungers are freely slidable within the bore of said holding means.