SUMMARY OF THE INVENTION

According to the present invention there is provided an injecting apparatus for injecting a fluid under pressure, the injecting apparatus including: a body, piston means movable in the body under the action of externally applied fluid pressure, the piston means being operable to compress in a high pressure chamber, fluid to be injected the piston means being movable against the action of fluid pressure in a low pressure chamber whereby the movement of the piston means is selectively controllable by controlling the fluid pressure in the low pressure chamber, and an injection valve and an associated injection orifice in fluid communication with the high pressure chamber whereby high pressure fluid from the high pressure chamber can be injected through the injection orifice upon opening of the injection valve.

Preferably the injection valve which controls injection of high pressure fluid through the orifice is selectively controllable in its operation. The injection valve may include a valve member movable against the action of fluid pressure in a control chamber, the fluid pressure in the control chamber being selectively controllable to control operation of the injection valve. The control chamber is preferably in fluid communication with the low pressure chamber whereby an increase in fluid pressure in the low pressure chamber to resist movement of the piston means also increases the fluid pressure in the control chamber resisting opening of the injection valve.