See Figure 1
The diesel engine fuel system consists of the fuel tank, fuel line, feed pump, fuel filter, injection pump, injector lines, nozzle holders and nozzles, leak-off lines, and the fuel return line.
The feed pump draws fuel from the tank through the fuel line. It passes through the fuel filter mounted at the back of the intake manifold and enters the injection pump. At the proper intervals, the injection pump forces fuel at high pressure into the injector lines. High-pressure fuel is sprayed into the combustion chambers through the nozzles. Fuel not used during operation is drawn off the leakoff lines and returned to the fuel tank by the fuel return line.