Downstream of the valve 106 there is an outlet port 110 through which pressure relieving flow can take place when the valve 106 is open. Associated with the outlet port 110 or downstream thereof there is preferably provided an adjustable flow restriction means to enable selective control of the rate of pressure relieving flow through the outlet port 110, the adjustable flow restriction comprising a governor arrangement such as shown in FIG. 2.

FIG. 4 showns an alternative injector control arrangement located at the rear body 13 of the injector, although the control arrangement may be a separate unit connected in the fluid pressure relief path from the low pressure chamber 37. In the embodiment in FIG. 4, pressure relief from the chamber 37 is provided through a fluid pressure relief path comprising a first chamber 120 which communicates with an intermediate chamber 121 through a pressure compensating means 122 comprising a restriction 123 (FIG. 5) shown in the form of a slot provided within sleeve 124. Inside the sleeve there is provided a shuttle valve member 125 having a head 126 which progressively closes or opens the slot 123 as the shuttle valve 125 moves within the sleeve 124.