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fuel pump[′fyül ‚pəmp]
A mechanical or electrical pump for drawing fuel from a storage tank and forcing it to an engine or furnace. The type of pump chosen for a given fuel depends to a great extent on the volatility of the liquid to be pumped. In a gasoline engine the fuel is highly volatile at ambient temperature. Therefore, the fuel line is completely sealed from the tank to the carburetor or fuel-injection system to prevent escape of fuel and to enable the pump to purge the line of vapor in the event of vapor lock—a condition in which the fuel vaporizes owing to abnormally high ambient temperature. See Carburetor, Fuel injection, Fuel system
Most carbureted gasoline engines use a spring-loaded diaphragm-type mechanical pump which is normally actuated by a rocker arm or pushrod that rides on an eccentric on the engine camshaft. Electric motor‐driven and solenoid-operated diaphragm pumps and plunger pumps are also available that can be mounted near the main fuel tank to minimize vapor lock in the fuel lines. Many gasoline-engine vehicles have a submersible electric fuel pump, which serves as the main supply pump, located in the fuel tank. In some fuel-injection systems, the in-tank pump is used as the supply pump for a high-pressure fuel-injection pump. The in-tank pump may be of the gear, plunger, sliding-vane, or impeller type.
Diesel engines normally use a gear, plunger, or vane-type pump to supply fuel to the injection pump. In the diesel engine, where fuel is injected at high pressure through an injection nozzle into the highly compressed air in the combustion chamber, a plunger or piston serves as its own inlet valve and as the compression member of the injection pump. When the required high pressure is reached in the injection nozzle, a spring-biased needle valve opens and fuel sprays into the combustion chamber. In an oil-fired furnace, although nozzle pressures need not be so high as in diesel engines, a piston pump is also used to provide positive shutoff of the fuel line when the pump stops. See Diesel engine