Fig. 4   

FILTER

 

Operating Principles

Petrol from the fuel tank enters the filter unit through the inlet. It then passes through the filter element into the base, and upwards through the centre tube, leaving the filter unit by means of the outlet. Abrasive particles are retained by the filter element. In the latest type of agglomerator-sedimenter (Figure 4), droplets of water, which are forced through the pores of the filter-agglomerator medium, collect together and form large drops. These are then separated by sedimentation and accumulate in the base of the transparent housing. The level in the filteragglomerator unit must not be allowed to rise above the base of the element.

Fig. 5   

ELECTRIC MOTOR

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.

PUMP

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 (730.00 kN/m2).

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.