Lesson 2/Learning Event 1
The fuel delivered by the injection pump flows through the high-pressure line and enters the nozzle holder
inlet. It passes through the edge filter, flows through the ducts in the holder and nozzle body, and flows
down into the pressure chamber of the spray nozzle above the valve seat.
There, the pressure of the fuel oil acts on the differential area of the nozzle valve. At the moment when
the pressure of the fuel exceeds the pressure exerted by the adjusting spring, the nozzle valve is lifted off its
seat and the fuel is forced through the orifice and sprayed into the combustion chamber of the engine. The
nozzle valve returns to its seat after the injection pump has ceased to deliver fuel. The hydraulic opening
pressure of the spray nozzle may vary from 1,000 to 4,000 PSI, depending on engine combustion chamber
Because of the widely differing shapes of the fuel spray for various combustion chamber designs and because
of the wide range in engine power demands, a variety of nozzles are used with multiple-unit injection pump
systems. Essentially, there are two basic groups: pintle nozzles and hole nozzles. Pintle nozzles are
generally used in engines with precombustion, turbulence, or divided chambers. Hole nozzles are generally
used with open combustion chamber designs.
The nozzle holder holds the spray nozzle in its correct position in the engine cylinder, provides a means of
conducting fuel oil to the nozzle, and conducts heat away from the nozzle.