<P> Because of the need for positive injection into a very high - pressure environment, the pump develops great pressure--typically 15,000 psi (100 MPa) or more on newer systems . This is a good reason to take great care when working on diesel systems; escaping fuel at this sort of pressure can easily penetrate skin and clothes, and be injected into body tissues with medical consequences serious enough to warrant amputation . </P> <P> Earlier diesel pumps used an in - line layout with a series of cam - operated injection cylinders in a line, rather like a miniature inline engine . The pistons have a constant stroke volume, and injection volume (i.e., throttling) is controlled by rotating the cylinders against a cut - off port that aligns with a helical slot in the cylinder . When all the cylinders are rotated at once, they simultaneously vary their injection volume to produce more or less power from the engine . Inline pumps still find favour on large multi-cylinder engines such as those on trucks, construction plant, static engines and agricultural vehicles . </P> <P> For use on cars and light trucks, the rotary pump or distributor pump was developed . It uses a single injection cylinder driven from an axial cam plate, which injects into the individual fuel lines via a rotary distribution valve . Later incarnations such as the Bosch VE pump vary the injection timing with crankshaft speed to allow greater power at high crank speeds, and smoother, more economical running at slower revolution of crankshaft . Some VE variants have a pressure - based system that allows the injection volume to increase over normal to allow a turbocharger or supercharger equipped engine to develop more power under boost conditions . </P> <P> All injection pumps incorporate a governor to cut fuel supply if the crankshaft rpm endangers the engine - the heavy moving parts of diesel engines do not tolerate overspeeding well, and catastrophic damage can occur if they are over-revved . Poorly maintained and worn engines can consume their lubrication oil through worn out crankcase ventilation systems and' run away', causing increasing engine speed until the engine destroys itself . This is because most diesel engines only regulate their speed by fuel supply control and don't have a throttle valve to control air intake . </P>

The fuel injection timing in a distributor type pump is controlled by