In an electronic fuel-injected engine, the fuel for the injectors must be pressurized before the engine can be started, so an electric fuel pump is necessary.
An electric rotary pump can be located in the tank, or externally, on the underside of the body.
Gasoline enters at one end and leaves at the other, so it is always full. This lubricates the pump motor and keeps it cool. The pumping element is a roller-cell device driven by an electric motor. A rotor disc is mounted eccentrically in the pump housing. It has recesses around its edge, containing metal rollers. As the disc rotates, centrifugal force pushes them outward. This forms a rotating seal, and fuel is carried round in the cavities formed between the rollers. Because of the eccentric mounting of the disc, these cavities expand as they pass the inlet, and contract passing the outlet. This pressurizes the fuel and forces it into the fuel line.
The pump can also be an impeller type, which is less noisy.
For a short time after an engine is switched off, engine temperature keeps rising, and that can cause excess vapor in the fuel lines. This pump stops this, with a non-return valve on its outlet, which maintains the pressure in the fuel line during that short time.
If a fuel blockage occurs further along the fuel line, it can overload the pump motor, and make it overheat. So a high-pressure relief valve inside the pump lets fuel keep circulating.
When the pump is mounted externally, a low-pressure pump can be used to supply fuel to the main pump’s inlet. This low-pressure pump is mounted in the fuel tank. It’s a centrifugal type, and electrical, and it operates in the same way as the other high-pressure pump.
