An auxiliary fuel pump is a common component of airplanes with fuel-injected engines. As the name suggests, it’s designed to “pump” fuel to the engines. Upon reaching the engines, the fuel is mixed with air and ignited. This triggers the combustion process, allowing the engines to generate thrust.
Overview of Auxiliary Fuel Pumps
Auxiliary fuel pumps are devices that provide supplementary fuel pumping in aircraft. Also known as boost pumps, they ensure engines have sufficient fuel.
Most airplanes don’t rely on a single fuel pump. Rather, they have two fuel pumps: a primary engine-driven fuel pump and an auxiliary fuel pump. If the engine-driven fuel pump fails or is otherwise unable to transfer fuel to the engines, the auxiliary fuel pump will take over.
The main purpose of an auxiliary fuel pump is to provide consistent fuel pressure when the engine-driven pump can’t do the job effectively. Typically powered by electricity, it can be activated manually by the pilot or automatically by onboard systems.
How an Auxiliary Fuel Pump Works
Most auxiliary fuel pumps are electric, but some of them use different methods to transfer fuel to the engines. There are diaphragm fuel pumps, for instance, that feature a flexible diaphragm. As the diaphragm opens, fuel will pass through them.
There are also centrifugal fuel pumps. Typically found in larger airplanes, centrifugal fuel pumps feature rotating impellers. As the impellers turn, they push fuel to the airplane’s engines.
Finally, there are vane fuel pumps. Vane fuel pumps feature spinning vanes that force fuel through one or more hoses and to the airplane’s engines.
Why Airplanes Have an Auxiliary Fuel Pump
Being that airplanes already have an engine-driven fuel pump, you might be wondering why they have an auxiliary fuel pump. Auxiliary fuel pumps serve several purposes, one of which is redundancy. Aircraft components can fail — and fuel pumps are no exception. Even if the engine-driven fuel pump fails, though, the auxiliary fuel pump will ensure the engines have sufficient fuel.
Auxiliary fuel pumps often assist with starting an airplane’s engines. Engine-driven fuel pumps only work when the engines are running. Therefore, airplanes may use an auxiliary fuel pump to initially start the engines, at which point the engine-driven fuel pumps will kick in.
Another reason airplanes have an auxiliary fuel pump is to maintain fuel pressure. At high altitudes, the auxiliary fuel pump may transfer fuel to the engines to prevent vapor lock.
