DETROIT DIESEL 53
2.2
FUEL PUMP
The positive displacement gear type fuel pump
(Fig. I) 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.
The fuel pump cover and body are positioned by
means of two dowels. The dowels aid in maintaining
gear shaft alignment. The mating surfaces of the pump
body and cover are perfectly flat ground surfaces. No
gasket is used between the cover and body since the
pump clearances are set up on the basis of metal-to-
Fig. 1. Typical Fuel Pump Assembly
metal contact. A very thin coating of sealant provides a
seal against any minute irregularities in the mating
surfaces. Cavities in the pump cover accommodate the ends of the drive and driven shafts.
also provided at the inlet and outlet positions of the gears. The small hole "A" permits the fuel oil in the inlet
side of 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. Pressurized fuel contacts the relief valve through hole
"B" and provides for relief of excess discharge pressures. Fuel re-enters the inlet side of the: pump through
hole "C" when the discharge pressure is great enough to move the relief valve back from its seat. Part of the
relief valve may be seen through hole "C". The 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. 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
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. Two tapped holes in the under side
of the pump body, between the oil seals, furnish a means of attaching tubing for draining off any leakage.
The drive and driven gears are a line-to-line to a .001" press fit on their shafts. The drive gear is
provided with a gear retaining ball to locate the gear on the shaft.
A spring-loaded relief valve incorporated in the pump body normally remains in the closed position,
operating only when pressure on the outlet side (to the fuel filter) reaches approximately 65 psi.
Operation
In operation, fuel enters the pump on the suction side and fills the space between the gear teeth which are
exposed at that instant. The gear teeth then carry the fuel oil to the discharge side of the pump and, as the
gear teeth mesh in the center of the pump, the fuel oil is forced out into the outlet cavity. Since this is a
continuous cycle and fuel is continually being forced into the outlet cavity, the fuel flows from the outlet cavity
into the fuel lines and through the engine fuel system under pressure.
The pressure relief valve relieves the discharge pressure by by-passing the fuel from the outlet side of
December, 1970 SEC. 2.2
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