It might seem like a really stupid question, But i'm getting into flying the FBW A320 in MSFS2020 and I have no idea what the fuel pumps are for in the A320, please may someone explain and help a newbie out? Thanks
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16$\begingroup$ What purpose do you imagine they might serve? What research have you done on this question? $\endgroup$– randomheadJun 22, 2022 at 21:34
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12$\begingroup$ What do they do in your car? $\endgroup$– JimJun 22, 2022 at 22:47
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12$\begingroup$ It's not a stupid question, fuel pumps in a car have an obvious purpose, but airplanes have multiple fuel tanks and sometimes have pumps for cross-fueling and balancing weight. $\endgroup$– GdDJun 23, 2022 at 16:32
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2 Answers
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What is the purpose of the fuel pumps in the A320?
Fuel for the A320 is located in each wing and a center fuselage tank. These fuel pumps are primarily used to provide positive pressure to supply the fuel to the engines. If the fuel pumps fail in a wing tank, suction valves allow fuel to flow via gravity to the engines. (no suction valves available for the center tank).
A more complex and comprehensive explanation regarding secondary uses of the fuel pumps is available if required, but it's a fairly simple principle.
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2$\begingroup$ I'd be interesting in hearing about the secondary uses. $\endgroup$– forestJun 23, 2022 at 23:48
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4$\begingroup$ @forest- As stated by GdD's comment to the OP's question (above), the fuel pumps are also used for cross-feeding fuel from a wing tank for use by the other engine (e.g. when an engine is shut down and fuel in the wing tank used by that engine is no longer being used, that fuel can be used by the operating engine [thru cross-feeding] to keep both tanks balanced). Also the pumps can be used for de-fueling a tank. A few other uses as well. $\endgroup$– user22445Jun 24, 2022 at 1:03
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Non-Airbus specific: You normally have an engine driven fuel pump (EDP) at the engines, supplemented by electric boost pumps in the wing tanks. The engine driven pump provides direct pressure to the fuel control system on the engine itself, always well beyond what the engine needs, with excess fuel continuously returned to the tank, usually referred to as "motive flow".
The electric pumps in the wing tanks are to pressurize the lines to the EDP inlet so the EDP doesn't have to suck fuel all the way from the wing in critical situations, and they're also there as a backup to the EDP itself. You may also have electric pumps to handle fuel transfer and crossfeed functions.
The return "motive flow" from the EDP is also used to run ejector scavenge pumps, venturi pumps with no moving parts, like those plastic gadgets you hooked up to a garden hose to drain waterbeds back in the day. The scavenge pumps draw fuel from the tank extremities to a "collector tank" usually a well at the inboard end of the larger tank, open to the rest of the tank at the top and kept always overflowing by the scavenge pumps, and within which the electric boost pump will normally reside.
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$\begingroup$ Your second paragraph seems to end in the middle $\endgroup$ Jun 24, 2022 at 3:02
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$\begingroup$ Missing period, and some finger trouble. Thanks. $\endgroup$– John KJun 24, 2022 at 4:23
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$\begingroup$ Is it necessary to pressurize the fuel lines so that the fuel does not vapourize with the low pressure of the suction? $\endgroup$ Jun 24, 2022 at 19:18
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1$\begingroup$ That's one benefit to having the boost pump running; resistance to vapour lock and you can have a minor leak in the plumbing between them and the EDP still gets its feed. Some airplanes may run boost pumps all the time, some only in departure/arrival configuration or some such. $\endgroup$– John KJun 24, 2022 at 22:46