The A320 has 5 fuel tanks and two very small vent tanks. The vent tanks act as overflow and ventilation tanks. If fuel is in the center tank, that fuel will be used first. Once that tank is empty, fuel is then pumped from the main tanks to the engines.
The center and main tanks have 2 fuel pumps each. One pump is sufficient to ensure fuel supply to the engine. Should both pumps in a tank fail, the engines can still operate by a so called "Gravity Fuel Feeding". However this does not apply to the center tank! Should both center tank pumps fail, the center tank fuel will become unusable.
There is one Crossfeed valve installed, which has two electric motors to ensure its operation. An open crossfeed valve allows an engine to be fed by the opposite main tank.
The total usable fuel of the A320 = 18728 kg ~ 8 h
Outer Tanks are relatively small but due to their leverage they:
- Reduce bending of wing surface
- Reduce wing fluttering
- Lower the structural weight at the wing root
The fuel from those tanks cannot be used directly, since the fuel transfers to the respective inner tank via fuel transfer valves. The fuel from the outer tank will transfer automtically into its respective main tank via a transfer valve. Both transfer valves open simultaneously when one main tank reaches - 750 kg.
The fuel is also used for the cooling of the engine oil and the integrated drive generators (IDG).
Engine Oil Cooling
For engine oil cooling the fuel is passed through a servo fuel heater and a fuel/oil heat exchanger, before it goes into the Hydro Mechanical Unit. This unit is responsible for regulating the fuel flow to the engine and also regulate the hydraulic signals for other systems.
For IDG cooling, some fuel is taken from the HMU and passes through the IDG Oil Cooler, before it then is returned to the Outer Fuel Tanks. This fuel return system is very clever and uses different return fuel flows and mixes them with cold fuel to ensure a relative constant oil temperature for the engine and IDG oil. There are situations where actually no fuel is returned to the outer tanks.
Only for Flight-Simulation!