Via the high-pressure pump and the supply pipe the fuel reaches the lower section of the injector (nozzle). There, the fuel applies pressure on a narrow, sloping ring of the injector needle (pressure shoulder). The very high pressure would be sufficient to move the needle against its spring upwards. Yet, the same pressure is also applied on top via a throttle on the full cross section of the needle, keeping it closed.

The room above the nozzle needle, filled with high pressure fuel, is opened by an electrically headed valve towards its return pipe. More fuel is flowing out of the injector than is coming in at the throttle. The pressure applied on top is thereby becoming clearly smaller than the pressure on the shoulder, thereby opening the nozzle needle.

As soon as the electrically headed valve is without current, the run-off of the fuel is interrupted. The pressure above the needle builds up again, closing the nozzle. 08/08