EP0594349A1 — Device to prevent refilling of a hypodermic syringe

USPTO Abstract

The present invention provides an anti-backup device which prevents the nut (10) from moving up the threaded piston (5) at the end of the dose by rotating in the opposite direction of that in which the nut (10) moves up the position to set the new dose by rotating dose knob. In this way, it is assured that movement of the nut up the threaded piston is due to rotating the dose knob (15) in the proper direction. The preferred device is a pawl (25) mounted on the end of a flexible arm (32) of the nut which cooperates with slots (26) on the inside of the syringe barrel (27). The nut (10) also has an incline surface (28) at the end which mates with an incline surface (29) in the barrel (27) and the mating of these surfaces at the end of the dose forces the pawl (25) into a slot (26) and prevents rotation of the nut (10) in the wrong direction, thus preventing refilling of the syringe.