The injecting system in another embodiment may be characterised in that the fluid pressure relief path includes a high speed solenoid valve operative to open and close the fluid pressure relief path in response to actuation signals, the governor means being located downstream of the solenoid valve and being operative to adjustably limit in continuous increments the flow of fluid through the fluid pressure relief path.

Possible and preferred features of the present invention will now be described with particular reference to the accompanying drawings. However it is to be understood that the features illustrated in and described with reference to the drawings are not to be construed as limiting on the scope of the invention. In the drawings: