TM 5-3895-359-14&P
FUEL PUMP
The positive displacement gear-type fuel pump (Fig. 1)
The fuel pump cover and body are positioned by two
transfers fuel from the supply tank to the fuel injectors.
dowels. The dowels aid in maintaining gear shaft
The pump circulates an excess supply of fuel through
alignment. The mating surfaces of the pump body and
the injectors which purges the air from the system and
cover are perfectly flat ground surfaces. No gasket is
cools the injectors. The unused portion of fuel returns to
used between the cover and body since the pump
the fuel tank by means of a fuel return manifold and fuel
clearances are set up on the basis of metal-to-metal
return line.
contact. A very thin coat of sealant provides a seal
against any minute irregularities in the mating surfaces.
The fuel pump is attached to the rear end plate cover of
Cavities in the pump cover accommodate the ends of
the blower assembly with three nylon patch bolts which
the drive and driven shafts.
prevents the oil in the blower cover from seeping out
around the bolt threads. The pump is driven off the end
The fuel pump body is recessed to provide running
of the blower lower rotor by means of a drive coupling
space for the pump gears (Fig. 3). Recesses are also
fork attached to the end of the pump drive shaft and
provided at the inlet and outlet positions of the gears.
mating with a drive disc attached to the blower rotor as
The small hole "A" permits the fuel oil in the inlet side of
shown in Fig. 2.
the pump to lubricate the relief valve at its outer end
and to eliminate the possibility of a hydrostatic lock
which would render the relief valve inoperative.
Fuel pumps are furnished in left-hand or right-hand
Pressurized fuel contacts the relief valve through hole
rotation. Since the engine is right-hand rotation, a right-
"B" and provides for relief of excess discharge
hand pump is used' and is stamped "RH IN". These
pressures. Fuel reenters the inlet side of the pump
pumps are not interchangeable, nor can a pump made
through hole "C" when the discharge pressure is great
for one rotation be rebuilt for the other rotation since the
enough to move the relief valve back from its seat. Part
relief valve can be installed in only one position in the
of the relief valve may be seen through hole "C". The
pump body.
cavity "D" provides escape for the fuel oil which is
squeezed out of the gear teeth as they mesh together on
the discharge side of the pump. Otherwise, fuel trapped
at the root of the teeth would tend to force the gears
apart, resulting in undue wear on the gears, shafts, body
and cover.
Two oil seals are pressed into the bore in the flanged
side of the pump body to retain the fuel oil in the pump
and the lubricating oil in the blower timing gear
compartment (Fig. 4). The oil seals are installed with
the lips of the seals facing toward the flanged end of the
pump body. A small hole "E" (Fig. 3) serves as a vent
passageway in the body, between the inner oil seal and
the suction side of the pump, which prevents building up
any fuel oil pressure around the shaft ahead of the inner
seal.
However, in this application, where the fuel supply tank
is mounted at a level higher than the fuel pump on the
Fig. 1 - Typical Fuel Pump Assembly
engine, the inner seal is installed with the lip of the seal
facing the gear pocket (Fig. 4). In this case, the inner
seal will prevent seepage of fuel oil along the pump
shaft and out the drain hole in the pump body, especially
when the engine is shut down. Fuel pumps with this
seal arrangement are identified by a "star" stamped on
the ground face of the pump cover.
10-3-29
