Patent ID: 7357781

Claim:
A needleless injector comprising: a barrel for receiving an injectable liquid from a source thereof; a nozzle in one end of said barrel for discharging liquid from said barrel; a plunger slidable in said barrel for movement between a retracted position in which liquid is drawn into said barrel between said nozzle and said plunger and an extended position in which liquid is discharged through said nozzle; a piston slidable in said barrel for retaining said plunger in the retracted position and movable under fluid pressure to move said plunger to the extended position; a retractor in said barrel for moving said plunger to the retracted position when said piston is retracted; a coupler connecting said retractor to said plunger permitting sliding of said piston in said barrel against said plunger to move the latter to the extended position, and for drawing the plunger to the retracted position when the piston and retractor are moved in a direction away from said nozzle to the retracted position; a first valve for introducing fluid under pressure into said barrel alternately on one side of said piston to move the piston and plunger from the retracted to the extended position to discharge liquid through said nozzle, and on a second side of said piston to return the piston and plunger to a retracted position in which injectable liquid is drawn into the barrel between said nozzle and said plunger; a trigger for operating said first valve to cause said plunger to move from the retracted to the extended position and then back to the retracted position each time the trigger is operated; a stop in a second end of said barrel remote from said one end for limiting movement of the piston when the plunger anti piston move to the retracted position; and a magnet in said piston releasably retaining the piston and plunger in the retracted position until the trigger is operated.