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 TM 55-1905-221-14-2
5-18. FUEL INJECTOR (Continued).
c. Combustion required for satisfactory engine operation is obtained by injecting, under pressure, a small quantity
of accurately metered and finely atomized fuel oil into the cylinder.
d. The continuous fuel flow through the injector:
Prevents air pockets in the fuel system.
Provides a coolant for those injector parts subjected to high combustion temperatures.
e. Both the injector plunger and plunger bushing are marked with identical part numbers to properly identify them
as mating parts. Therefore, if either plunger or bushing requires replacement, both must be replaced as an assembly.
CAUTION
Do not intermix the needle valve injectors with the other types of injectors in an
engine.
f. Each fuel injector has a circular disc pressed into a recess at the front side of the injector body for identification
purposes. The identification tag indicates the nominal output of the injector in cubic millimeters.
g. Fuel under pressure enters the injector from a fuel manifold. Motion of the rocker arm allows the injector to
release a spray of fuel into a cylinder. A control rack on the side of the injector controls the amount of fuel being
dispensed, and the speed of the engine. The injector control rack 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. Excess fuel exits the injector and is returned to a fuel
manifold. The fuel then returns to the fuel tank.
h. The fuel injector is one of the most important and precisely built parts of the engine. The injection of the correct
amount of fuel into the combustion chamber at exactly the right time depends upon this unit. Because the injector
operates against high compression pressure in the combustion chamber, efficient operation demands that the injector
assembly is maintained in first-class condition at all times. Proper maintenance of the fuel system, and the use of the
recommended type fuel filters and clean water-free fuel, are the keys to trouble-free operation of the injectors.
5-400
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