Single use disposable needleless injector

An operable single use needleless hypodermic injector comprising:

• an elongate housing having a proximal end, a distal end, a hollow bore therethrough and a longitudinal axis;
• a reservoir at said distal end of said housing, said reservoir having a generally cylindrical chamber defining a longitudinal axis for containing an injectable liquid, said chamber being axially aligned with said longitudinal axis of said housing, said reservoir having a first open end adjacent said housing, a resilient stopper mounted slidably within said chamber, said stopper for sealing said chamber and for ejecting the liquid from said chamber, and a distal second end of said reservoir having an orifice in fluid communication with said chamber, said orifice serving to form a stream of the liquid when said stopper is moved distally in said chamber;
• and
• an elongate piston mounted for axial movement within said bore having a proximal end and a distal end, said injector having biasing means for axially biasing said piston to said distal end of said housing, said piston having an armed position wherein said piston is positioned proximally in said housing in opposition to said biasing means, said biasing means thereby having potential energy, retention means for retaining said piston in said armed position, release means for releasing said piston from said armed position and allowing said energy of said biasing means to urge a distal axial movement of said piston, said movement of said piston to engage and to cause a distal axial movement of said stopper through said chamber thereby ejecting the liquid through said orifice, so that the stream of the liquid being formed at said orifice will make a hypodermic penetration when said orifice is placed adjacent dermal tissue, and means for preventing said piston from being retained in said armed position after said release means is released.