The present invention provides a needle-free injector for delivering a medicament under pressure into an animal or human, the injector having a charging mechanism comprising a threaded shaftnut member combination. It comprises an inflatable chamber, a compression cell, and tubes to carry a fluid between them. The transducer comprises at least two sensorially active functional groups synchronously using sensorially active groups or sub-groups which are locally offset in relation to each other by a local phase \u03c6 in order to scan the moving scale, and the functional groups comprise means enabling at least two independent partial signals S1=V*sin and S2=\u2212V*sin+\u03c6) to be produced. The fuel inlet conduit and fuel outlet conduit, each in the respective portions immediately adjacent to the valve chamber, have a gradually tapered cross section compared to the cross section of the remaining regions of the fuel inlet conduit and fuel outlet conduit. The invention also provides methods for the detection, prevention and treatment of pathological conditions resulting from bacterial infection.