What Are Aircraft Fuel Pumps & Their Common Types?
Aircraft rely on a fuel system to pump, manage, and deliver the fuel that powers flight. In aircraft fuel systems, the propulsion and auxiliary power units (APU) drive movement. Similar to the human circulatory system, fuel is pumped through the body of the aircraft like blood through the body. Fuel travels through fuel lines, and the system can be monitored by the pilot through the use of a fuel control valve. This valve sometimes functions as both a shut off and selector valve, that of which the pilot uses to choose which engine to fuel. In some aircraft, these functions belong to separate valves. The gascolator is the part of the fuel system that functions as a filter to ensure the fuel is pure and is not contaminated. This instrument should be manually opened and drained from the ground. The level of pressure and flow rate of fuel throughout aircraft is important as it relates directly to the craft’s ability to function.
All fuel systems consist of a gravity feed fuel tank connected to the aircraft’s engine. Meaning, the larger the aircraft is, the more fuel tanks it might require. A fuel pump is an important component of tanks situated below the carburetor, serving to feed the engines, allow for refueling and defueling, isolate various tanks, and occasionally dump fuel to alter the aircraft’s gravity.
Aircraft fuel pumps are necessary for when gravity alone cannot regulate a simple fuel pump system. Similar to the gravity flow system, the fuel pump system begins at the fuel tank. The fuel first travels to the selector valve in the cockpit, which then sends the fuel to the filter. At this point, the fuel is regulated by a backup electrical pump or a vane-type fuel pump to maintain flow and pressure through the use of an electric or hand-operated mechanism. The fuel then reaches the engine driven pump which can be considered the heart of the system. Here, the engine driven pump serves as the primary fuel pressure source and it is fastened to an auxiliary pad on the engine crankcase. This determines when it supplies fuel to the carburetor or fuel injector under pressure, and certain aircraft are legally required to have a backup auxiliary fuel pump. The pressure of the entire system is measured and monitored by a fuel pressure gauge, upon which the pilot relies.
The engine-driven fuel pump functions during operation to mechanically distribute the correct amount of fuel to the carburetor or fuel injector. The standard model of fuel pump for small aircraft is the AC diaphragm-type aviation fuel pump which is self priming and can withstand chemicals used in modern fuels. The backup pump is referred to by many names, including the auxiliary pump, the booster pump, and the electric pump. This pump fights vapor formation, compensates for failures of the main pump, and aids in take-off and landing procedures. An example of these pumps is the wobble pump, which the pilot controls manually to bypass certain automatic functions of the aircraft fuel system.
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