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Operation 

The one-way feeding system for Diesel fuel injection pumps is an original Lombardini design. Its main distinguishing features are the absence of the traditional fuel annular chamber around the plunger barrel and the use of a non-return valve on the fuel return line.

On the Lombardini pump the fuel is fed directly to the plunger chamber through a side bore when the plunger is at its bottom dead center. At the end of the delivery stroke (upwards), all the excess fuel is discharged through a second bore to the return line, while the inlet bore remains closed by the plunger itself.

A helical groove on the plunger will uncover the discharge bore according to the plunger rotation. After passing the one-way valve, the overflow returns to the fuel tank. During the plunger down stroke, the fuel in the return line cannot be sucked back because of the valve.

This system avoids fuel emulsion in the plunger chamber and consequent incorrect fuel feed and injection timing. In fact, during the high velocity discharge phase, fuel vaporization can take place, originating foam which, differently from traditional systems, is rapidly taken away by the flow. Moreover, when the plunger is at rest position, the chamber is not only filled but also scavenged by a continuous fuel flow, if a feed pump is provided in the inlet line.

By actuating a solenoid valve on the fuel line at the pump inlet an immediate engine stop occurs due to the absence of the annular chamber (reduced fuel volume) and the one-way fuel flow.