Metering of the fuel is accomplished by an upper and lower helix machined in the lower end of the injector
plunger. Figure 3 illustrates the fuel metering from no load to full load by rotation of the plunger in the bushing.
Figure 4 illustrates the phases of injector operation by the vertical travel of the injector plunger.
The continuous fuel flow through the injector serves, in addition to preventing air pockets in the fuel system, as
a coolant for those injector parts subjected to high combustion temperatures.
To vary the power output of the engine, injectors having different fuel output capacities are used. The fuel
output of the various injectors is governed by the helix angle of the plunger and the type of spray tip used.
Refer to Fig. 5 for the identification of the injectors and their respective plungers and spray tips.
Since the helix angle on the plunger determines the output and operating characteristics of a particular type of
injector, it is imperative that the correct injectors are used for each engine application. If injectors of different
types are mixed, erratic operation will result and may cause serious damage to the engine or to the equipment
which it powers.
Do not intermix the needle valve injectors with other types of injectors in an engine.
Each fuel injector has a circular disc pressed into a recess at the front side of the injector body for identification
purposes (Fig. 5). The identification tag indicates the nominal output of the injector in cubic millimeters.
Each injector control rack (Fig. 2) is actuated by a lever on the injector control tube which, in turn, is connected
to the governor by means of a fuel rod. These levers can be adjusted independently on the control tube, thus
permitting a uniform setting of all injector racks.
The fuel injector combines, in a single unit, all the parts necessary to provide complete and independent fuel
injection at each cylinder.
Fuel, under pressure, enters the injector at the inlet side through a filter cap and filter (Fig. 2). From the
Figure 3. Fuel Metering from No Load to Full Load.
Phases of Injector Operation
Through Vertical Travel of Plunger