The electric motor which drives the fuel pump is
a 12 volt high performance permanent magnet machine. The drive is
transmitted to the pump gears by means of a nylon coupling.
After passing through the filter unit, fuel enters the pump by means
of the inlet. (To prevent dirt from entering the system, when the fuel
pipes are removed, there is a nylon gauge strainer fitted in the pump
inlet). The two spur-type gears are rotated by the action of the electric
motor. As the gears rotate, fuel is expelled through the pump outlet at a
pressure depending on the setting of the relief valve, normally 106 lbf/in2
There are four sealing units in the fuel pump. A small
shaft seal prevents the entry of fuel into the electric motor. The sealing
properties are maintained by means of fuel, which is directed on it by the
nylon coupling. (A “tell-tale” pipe in the motor end bracket indicates
whether the fuel has passed this seal.)
Leakage of fuel from the pump is prevented by three
sealing rings, one between the pump body and the end bracket of the motor,
and the other two between the individual plates of the pump body.
In spite of its compact size, the fuel pump (Figure 5)
is very powerful, and is capable of delivering a minimum of 16 gallons
per hour at 100 lbf/in2 (689.50 kN/m2) with a current consumption
of approx. 5A. The pump must have sufficient capacity to supply the
extra fuel required during starting. Researches have shown that three
times the normal amount of fuel may be required at 00F (-17.70C) to ensure
a reasonably rapid start.
Note: If for any reason
the fuel pump is removed from the engine, it must be replaced in the same
position as originally fitted.