The injector shown in FIG. 3 is in most respects the same as the injector shown in FIG. 1 and the same reference numerals are used for corresponding parts.

Different features in FIG. 3 include the modified needle valve 70 which, instead of a conical tip, includes a blunt nose portion 70a which substantially fills the "sack" 72 which is a small space immediately upstream of the orifice 68. The fuel remaining in the sack 72 in prior injectors was sometimes a cause of continued fuel introduction into the cylinder after the desired cut off point.

Also in FIG. 3, the spacer 67 is provided with a non-return valve 100 arranged to allow the flow from the control chamber 78 to the low pressure chamber 37 but preventing a shock loading at any time from being transmitted into the chamber 78.

In FIG. 3, the inlet 15 is shown in a different location with a relatively small inlet valve 16 allowing fuel under low pressure to pass from the inlet 15 to an inlet manifold 102 which encircles the body 10 and enables fluid to pass from the annular manifold space 103 through passages 104 to the low pressure chamber 37.

Also in FIG. 3, there is provided a high speed solenoid 105 having an associated valve member 106 arranged to selectively close the outlet 20. The solenoid 105 can be energised under the control of an electrical switching means 107 by means of which the time of commencement of injection is controllable and also the length of the period of injection is also controllable. In particular, the opening of the valve 106 by solenoid 105 under the control of the control means 107 enables the injection to commence. Prior to opening of the valve 106 the piston assembly 30, 35 is effectively hydraulically locked against movement. Similarly, closing of the valve 106 will again lock the piston assembly 30, 35 against movement thereby terminating the injection.