2.2
DETROIT DIESEL 53
FUEL P U M P
The positive displacement gear type fuel pump
(Fig. 1) transfers the fuel from the supply tank to the
fuel injectors. The pump circulates an excess supply of
fuel through the injectors which purges the air from
the system and cools the injectors. The unused portion
of fuel returns to the fuel tank by means of a fuel
return manifold and fuel return line.
On the In-line engine, the fuel pump is mounted on
the governor weight housing and is driven through a
drive coupling by the governor weight shaft.
Fig. 1 Typical Fuel Pump Assembly
compartment (Fig. 1). 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. 2) serves as a
The fuel pump cover and body are positioned by
vent passageway in the body, between the inner oil
means of two dowels. The dowels aid in maintaining
seal and the suction side of the pump. which prevents
gear shaft alignment. The mating surfaces of the
building up any fuel oil pressure around the shaft
pump body and cover are perfectly flat ground
ahead of the inner seal. Two tapped holes in the under
surfaces. No gasket is used between the cover and
side of the pump body, between the oil seals, furnish a
body since the pump clearances are set up on the basis
means of attaching tubing for draining off any
of metal-to-metal contact. A very thin coating of
leakage.
sealant provides a seal against any minute irregulari-
ties in the mating surfaces. Cavities in the pump cover
The drive and driven gears are a line-to-line to a
accommodate the ends of the drive and driven shafts.
.001 " press fit on their shafts. The drive gear is
provided with a gear retaining ball to locate the gear
The fuel pump body is recessed to provide running
on the shaft.
space for the pump gears (Fig. 2). Recesses are also
provided at the inlet and outlet positions of the gears.
A spring-loaded relief valve incorporated in the pump
The small hole "A" permits the fuel oil in the inlet
body normally remains in the closed position,
side of the pump to lubricate the relief valve at its
operating only when pressure on the outlet side (to the
outer end and to eliminate the possibility of a
fuel filter) reaches approximately 65 psi.
hydrostatic lock which would render the relief valve
inoperative. Pressurized fuel contacts the relief valve
Operation
through hole "B" and provides for relief of excess
discharge pressures. Fuel re-enters the inlet side of the
In operation, fuel enters the pump on the suction side
pump through hole "C" when the discharge pressure is
and fills the space between the gear teeth which are
great enough to move the relief valve back from its
exposed at that instant. The gear teeth then carry the
seat. Part of the relief valve may be seen through hole
fuel oil to the discharge side of the pump and, as the
"C". The cavity "D" provides escape for the fuel oil
gear teeth mesh in the center of the pump, the fuel oil
which is squeezed out of the gear teeth as they mesh
is forced out into the outlet cavity. Since this is a
together on the discharge side of the pump. Otherwise,
continuous cycle and fuel is continually being forced
fuel trapped at the root of the teeth would tend to
into the outlet cavity, the fuel flows from the outlet
force the gears apart, resulting in undue wear on the
cavity into the fuel lines and through the engine fuel
gears, shafts, body and cover.
system under pressure.
Two oil seals are pressed into the bore in the flanged
The pressure relief valve relieves the discharge
side of the pump body to retain the fuel oil in the
pressure by by-passing the fuel from the outlet side of
pump and the lubricating oil in the blower timing gear
December, 1970 SEC. 2.2 Page 1
