Abstract: A needle-free injector, and method of using said injector, for injecting variable, discrete doses of liquids intradermally or transdermally into a subject in need thereof, are provided. The injector comprises a barrel having a front section, an intermediate section and a rear section; and a cap having a rear end connectable to the front section of the barrel and rotatable about the front section of the barrel, the cap having a discharge end for receiving a cartridge containing the liquid to be injected, wherein rotation of the cap about a longitudinal axis of the front section of the barrel adjusts the dose of liquid to be discharged from the cartridge by the injector in iscrete dose units. A piston cap is also provided for adjusting the force of the impact of an injector piston on a plunger on the cartridge.

Abstract: A disposable syringe for use in a needleless injector includes a tubular body with an open rear end, a closed front end containing an injection orifice, a chamber in the body for receiving a liquid and a plunger slidable in the chamber for pushing the liquid out of the orifice. A tip is provided on the inner end of the plunger for separation from the remainder of the plunger to block the orifice when the plunger is retracted after an injection, whereby the syringe cannot be re-used.

Abstract: A disposable nozzle for use on the discharge end of the barrel of a needleless injector is threaded onto the front end of a holder mounted in the barrel. A resilient detent extending outwardly at an acute angle from the inner wall of a recess in the rear end of the nozzle repeatedly enters and exits notches in a sleeve on the holder when the nozzle is mounted on the holder providing an audible signal that the nozzle has not been used. Reverse rotation of the nozzle during removal from the holder results in breaking of the detent. Thus, mounting of a used nozzle on the holder would not be accompanied by a signal that the nozzle is unused.

Abstract: A pistol-shaped needleless injector includes a readily replaceable barrel (36) in the front end thereof facilitating adjustment of the dosage administered using the injector. A disposable nozzle (98) mountable on a holder (97) extending outwardly from the front discharge end of the barrel (36) provides an indication that the nozzle (98) has been used and should be discarded.

Abstract: A needleless injector syringe includes a tubular barrel containing a first chamber for receiving a liquid, a nozzle on a front end of the barrel, a piston which drives a plunger for discharging the liquid through the nozzle, a second chamber in which the piston slides, a third chamber in fluid communication with the second chamber for receiving gas from said second chamber during forward movement of the piston, and for carrying gas to the second chamber to cause the piston to retract, and a breach plug closing a rear end of the barrel for directing gas under pressure alternately against the rear end of the piston and to the third chamber for driving the piston between the discharge position and a retracted position.

Abstract: A needleless injector syringe includes a tubular barrel containing a first chamber for receiving a liquid, a nozzle on a front end of the barrel, a piston which drives a plunger for discharging the liquid through the nozzle, a second chamber in which the piston slides, a third chamber in fluid communication with the second chamber for receiving gas from said second chamber during forward movement of the piston, and for carrying gas to the second chamber to cause the piston to retract, and a breach plug closing a rear end of the barrel for directing gas under pressure alternately against the rear end of the piston and to the third chamber for driving the piston between the discharge position and a retracted position.

Abstract: A disposable syringe for use in a needleless injector includes a tubular body with an open rear end, a closed front end containing an injection orifice, a chamber in the body for receiving a liquid and a plunger slidable in the chamber for pushing the liquid out of the orifice. A tip is provided on the inner end of the plunger for separation from the remainder of the plunger to block the orifice when the plunger is retracted after an injection, whereby the syringe cannot be re-used.

Abstract: A pistol-shaped needleless injector includes a readily replaceable barrel (36) in the front end thereof facilitating adjustment of the dosage administered using the injector. A disposable nozzle (98) mountable on a holder (97) extending outwardly from the front discharge end of the barrel (36) provides an indication that the nozzle (98) has been used and should be discarded.

Abstract: A needleless injector includes a barrel for receiving an injectable liquid, a nozzle closing one end of the barrel containing an injection orifice, and a plunger and piston combination in the barrel. A valve admits gas under pressure into the barrel behind the piston. A trigger opens the valve to cause the piston to move against the plunger, and a magnet retains the piston in a rest position in the barrel until acted upon by the gas under sufficient pressure to cause the piston and plunger to move to an extended, discharge position.

Abstract: A needleless injector includes a barrel (5) for receiving an injectable liquid a nozzle (82) closing one end of the barrel (5) containing an injection orifice; a plunger (46) movable in the barrel (5) for forcing liquid out of the barrel (5); a piston (6); in the barrel (5) for forcing liquid out of the barrel (5); a piston (6) in the barrel (5) for movement under gas pressure to move the plunger (46); a valve (118) for admitting gas under pressure into the barrel (5) behind the piston (6); a trigger (116) for opening the valve (118) to cause said piston (6) to move against the plunger (46); and a magnet (10) for retaining the piston (6) in a rest position in said barrel (5) until acted upon by a gas under sufficient pressure to cause the piston (6) and plunger (46) to move to an extended, discharge position. For extra protection a sterile pad can be disposed between the injection orifice and the skin of a person or animal receiving an injection.

Abstract: A needleless hypodermic injector includes an elongated cylindrical casing defined by front and rear telescoping sections, with an injection orifice at the closed front end of the front section and a push button trigger at the rear end of the rear section. A piston slidably mounted in a cylinder in the front section of the casing moves rearwardly to define a medicine chamber for receiving medicine from a bottle directly or through a valve incorporated in the front end of the front casing section. The piston is moved rearwardly by an internally threaded collar on the externally threaded cylinder, the collar pressing against a bushing, which presses against disc springs in the rear section of the casing. A latch mechanism retains the bushing against the springs until the trigger is pressed, at which time the springs drive the piston forward to discharge the medicine from the chamber through the injection orifice.

Abstract: A pneumatic jet injector for needleless injection of a liquid medicine into the skin includes a pistol-shaped casing including a barrel, a handle and a trigger; a compression chamber in one end of the casing for a gas which is partially liquefied under pressure; a first piston movable in the casing against the gas; a charging liquid in the handle which is pumped against the first piston using the trigger and a second piston in the handle; a piston rod movable in the barrel with the first piston for creating a partial vacuum in the barrel for drawing medicine into the barrel through an inlet containing a one-way valve; a discharge orifice in one end of the barrel for discharging medicine into the skin of a user; and a safety catch in the handle for locking the first and second pistons in the loaded or charged position, and for releasing the pistons whereby at least a portion of the liquid in the compression chamber becomes gaseous moving the piston rod against the medicine to discharge the medicine through the