Used previously for heavier vehicles, they have only recently become operational in cars. The replacement types usually use a diaphragm arrangement like the mechanical pumps, except that it is actuated by an electrical solenoid. It uses a small turbine wheel driven by a constant speed electric motor. The entire unit is located in the fuel tank and submerged in the fuel itself. When the engine is running the pump pump operates continuously, thus exerting a constant pressure which supplies the maximum fuel demands of the engine. When less fuel is required, the pump does not deliver at full potential, because the turbine is not a positive displacement type like the mechanical pump. Consequently, the turbine will run without pumping fuel and so, needs no means of varying fuel delivery rate like its mechanical counterpart. Since the fuel can flow past the spinning turbine blades, there is no need for pump inlet and outlet valves nor is there any need to vary its speed. A relay for the electric fuel pump is used to complete the circuit to the fuel pump. This cuts off current to the fuel pump in the event of an accident
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