Fuel pump

A fuel pump is an essential component on a car or other internal combustion engined device. Fuel has to be pumped from the fuel tank to the engine and delivered under low pressure to the carburetor or under high pressure to the fuel injection system. Some fuel injected engines have two fuel pumps for this purpose: one low pressure/high volume supply pump in the tank and one high pressure/low volume pump on or near the engine.

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In earlier cars built before the late 1970s, the pump was mechanically driven by a lobe on the engine's camshaft and therefore bolted to the engine block. It created negative pressure to "suck" the gasoline through the lines. However, the negative pressure from the pump, in combination with heat from the engine and/or hot weather, could cause the gasoline to boil. The fuel pump, designed to pump liquid, not vapor, would be unable to suck more gasoline to the engine, which would cut out. This condition is known as "vapour lock". Also a suction pump could suck in air through (difficult to diagnose) faulty hose connections. A leaking connection in a pressure line will show itself immediately.

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Nowadays, the fuel pump is located inside of the fuel tank and is usually electric. It creates positive pressure in the fuel lines, pushing the gasoline to the engine. The higher gasoline pressure raises the boiling point. Placing the pump in the tank puts the component least likely to handle gasoline vapor well (the pump itself) farthest from the engine, submersed in cool liquid. Another benefit to placing the pump inside the tank is that it is less likely to start a fire. Though electrical components (such as a fuel pump) can spark and ignite fuel vapors, liquid fuel will not explode (see explosive limit) and therefore submerging the pump in the tank is one of the safest places to put it. In most cars, the fuel pump delivers a constant flow of gasoline to the engine; fuel not used is returned to the tank. This further reduces the chance of the fuel boiling, since it is never kept close to the hot engine for too long.

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The fuel pump is generally on whenever the car's ignition switch is in the "on" position. Depressing the gas pedal results in the throttle body opening on the engine (metering the air going in) rather than engaging the fuel pump. The ignition switch does not carry the power to the fuel pump, instead it activates a relay which will handle the higher current load. It is common for the fuel pump relay to become oxidized and cease functioning; this is much more common than the actual fuel pump failing.

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Some cars with an electronic control unit have safety logic that will shut the electric fuel pump off even if the ignition is "on" if there is no oil pressure, either due to engine bearing damage or a stalled engine in a car accident. In case of an accident this will also prevent fuel leaking from any ruptured fuel line. Other cars have an additional roll over valve, that will shut off the fuel pump in case the car rolls over.

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Car: CAR may stand for:...

Internal combustion engine: An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. A piston internal combustion engine works by burning hydrocarbon or hydrogen fuel that presses on a piston; and a jet engine works as the hot combustion p...

Fuel tank: A fuel tank is part of an engine system in which the fuel is stored and released into the engine. Fuel tanks range in size and complexity from the small plastic tank of a butane lighter to the multi-chambered cryogenic Space Shuttle external tank....

Fuel pump related Images and Photos (experimental)

Pump Room	Blue Pump	Blue Pump	Pump Up the Volume
Pump Up The Volume (DVD)	Fuel: Angels and Devils CD	Fuel: Angels and Devils CD	Pump Up the Volume 1990
Pump Up the Volume 1990	Water Pump with Dishes	Bed of Roses/Pump Up the Volume (DVD) (DBFE) (Multi-Title)	Snow-Covered Gas Pump on Historic Route 66