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How Aircraft Fuel systems work?

One of the most complex systems found on an aircraft is its fuel delivery system. This apparatus works continuously from takeoff to landing to ensure a continuous flow of fuel to the aircraft's engines. While fuel injection systems vary between aircraft types and individual planes, many of the components remain the same. Therefore, this article will focus on a simple fuel delivery system.

The Fuel Tank

The purpose of a fuel injection system is to precisely deliver an exact amount of fuel into the engine's cylinders. This injection must be timed perfectly and with a correct ratio of air to fuel. Injection systems begin with tanks that vary in number and size depending on the demands of the aircraft. What may surprise most is that not all the fuel stored in a fuel tank is usable. Up to several gallons of unusable fuel is used to trap contaminants that naturally settle at the bottom.

The Fuel Selector Valve

Another component of the fuel injection system that will vary significantly between aircraft is the fuel selector valve. The selector valve allows the pilot to pick which tank to draw fuel from. The caveat is, an aircraft cannot pull fuel from more than one tank at a time unless there is a mechanism installed to prevent vapor lock. Vapor lock occurs when air is allowed into the fuel line, creating an impassable "bubble" that interrupts the flow. Vapor lock could easily occur if the line were to pull from an empty tank without a safeguard in place.


Found at the lowest point in the injection system, the filtering region will contain mesh sheets  that remove even the smallest contaminants before the fuel reaches the engine.

Fuel Pump

Depending on the position in which the fuel tanks are placed, the aircraft may or may not need an engine-driven fuel pump. For example, the Cessna 206, which features a high wing design, will not need an engine-driven fuel pump as the lines are fed by gravity. In contrast, low-wing aircraft will require a pump to bring fuel up to the engine. In addition to the main fuel pump, an auxiliary electric-powered pump will provide additional pressure if vapor lock or other failure occurs.

Servo Regulator

Another crucial feature of the fuel injector system is the servomechanism regulator or "servo" for short. These devices adjust the fuel to air ratio by measuring the pressures of each. As there is a demand for greater thrust, the amount of air in the engine increases, which makes the servo react by pulling more fuel into the system.

Fuel Distributor

One of the final components where fuel travels before reaching the engine's cylinder is the fuel distributor. After being metered in the servo, the distributor will take the fuel-air combination and deliver it in equal amounts to the nozzles.

Fuel Nozzle

The last step in the fuel injection process is aeration and delivery to the engine for combustion. This task is accomplished by the nozzles, which spray an atomized fuel-air mixture under high pressure directly into the combustion cylinder.

A properly functioning fuel system is essential for the cost-efficient and safe operation of aircraft. If you are in search of high-quality fuel system components for your airplane, choose Purchasing Union as your distributor. With an inventory of over 2 billion new, obsolete, and hard-to-find aerospace parts, we are confident that we can help you find the exact item you require. Furthermore, as an AS9120B, ISO 9001:2015 certified and FAA AC 00-56B accredited distributor, we stand by the quality of our products. Browse our website or search using part number, CAGE Code, manufacturer, part type, or NSN today and see how Purchasing Union is defining the future of parts procurement.


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