Patent ID: 8070714

Claim:
A method of preparing a needleless syringe for use, the needleless syringe including a gas generator, a reservoir consisting of a tube closed by an upstream plunger stopper and a downstream plunger stopper between which a liquid active principle is to be contained, the reservoir being able to have a variable volume by moving the downstream plunger stopper in the tube, and an injection device, the method comprising: providing a variable volume of liquid active principle in the needleless syringe between the upstream plunger stopper and the downstream plunger stopper; arranging the downstream plunger stopper when the needleless syringe is ready for injection so that a free space is left between the downstream plunger stopper and the injection device that allows for acceleration of the liquid active principle prior to ejection from the injection device by the gas generator; forming a pyrotechnic charge by mixing a first powder and a second powder, the first powder having a dynamic vivacity greater than that of the second powder; and calculating a length of the free space so that the liquid active principle reaches the desired injection speed when entering the injection device, wherein the length of free space is variable.