Locking syringe with thread-release lock

Abstract

A locking syringe selectively operable in either of a freely reciprocating or a restricted, threaded mode. A trigger attached to the plunger includes internal threads on the interior of the barrel of the syringe and external threads located on the plunger on a spine slidable in a longitudinal slot in the plunger. A handle is affixed to the plunger, and a retraction bar is rigidly secured to the spine. The threads on the plunger may be retracted from engagement with the threads on the barrel, thereby placing the syringe in its freely reciprocating mode. The trigger, which is spring biased to engage the external and internal threads, employs a plurality of ramps and channels disposed at approximately the same angle to the longitudinal axes of the plunger and barrel as are the threads. A pawl is pivotally securable on the retraction bar at a position receivable into a pawl receiving aperture on the handle when the receiving bar is in its first position permitting reciprocating movement of the plunger. In this position, the pawl prevents the retraction bar from returning to its second position in which free movement of the plunger is precluded. Alternatively, toward the same end an open, a circumferential clip can be placed on the plunger to restrain sliding of the spine disposed therein, or a plug can be inserted into an aperture in the handle occupied by the retraction bar in its first position.