Oil refineries are complex operations which process multiple types of fuel. Each refinery determines the types of fuel they process, then creates the lines and adds the pumps and filters required to meet the specs of the product being processed. If you have ever looked at a photograph of a refinery, the complex series of lines look like some sort of work of modern art. While the lines look pretty much the same, the vertical filters required for aviation fuel standout. Aviation fuel is the cleanest and driest fuel on the market, and refineries that process this fuel must be up to the challenge of meeting the high specs and standards.
Aviation fuel, jet fuel, and avgas require vertical filtration to properly remove the water and contaminates naturally present in the fuel source. This requires a complex multi-stage vessel, designed to separate dirt, contamination, and water so that the fuel meets the unique specs required for ultra-clean aviation fuel. The vertical filters required for this advanced processing are always easy to spot. These combined vertical filtration and separators are placed in multiple points throughout processing. All filtration units must be proven to pass the required qualifying tests.
Just like automotive fuel, aviation fuel varies. The category of fuel being processed will determine the multi-stage vertical filtration points. Filters have to be advanced enough to deliver clean fuel, without removing the required:
This is all while separation dirt, water, and contaminants—and while before a filter can be placed on the market, it must meet the advanced API/EI specs—and be tested and pass a live inspection. Military-grade fuel is typically the most complex to process.
During flight, the higher altitude causes the temperature of the fuel tanks to decrease. If there is too much water present in the fuel, it will cause the water to precipitate and separate—creating condensation in the bottom of the tank. These droplets can freeze, and block the fuel inlet pipe. Even with aircraft fuel heaters designed as a backup, fuel must be dirt and particle. This is why there must be a process in place to minimize contamination after leaving the refinery. This means refineries must invest in contamination-free transport tanks, and that they must continue testing the fuel (visually or with a chemical test) to ensure it clean upon arrival.
While refineries are responsible for delivering contamination-free aviation fuel, they have no control over what happens once the fuel is delivered. This is why aircraft must also have filtration systems built-in. These systems primary focus is to ensure the fuel is dry, but they must also filter for dirt and particle containments.