A320 Center Tank Pumps

[dream747]

Hi all,

Quite often at the gate we get the Low Pressure warning on one or both of the center tank pumps when the fuel quantity in the center tanks are low (anything from 20kgs - 200Kgs). I am aware of the procedure in the FCOM to have the center tank pumps off in this case.

Just an observation, most of the time when we put the pumps back on after the engines are started, the warning goes away and the pumps run normally.

My question is, why does this happen? I would imagine the performance of the pumps are the same before or after engine start as long as they have power supplied to them. So why is it that they are able to run after engine start but detect low pressure at the gate with the same amount of fuel in the tanks?

Also, there are a few occurrences whereby the center tank pumps are in "crosslink green", where auto shut off is required but there are still an unusually high amount of fuel in the tanks. Highest I've seen is 210kg.

Does anyone have frequent experiences with this?

[Goldenrivett]

Hi dream747,

We had exactly what you described about 10 years ago.
Once we had almost 200 kgs of centre tank fuel which we could not use (due pump low pressure lights on when the pumps were running.) The fix was to put about 500 kgs of fuel into the centre tank. The higher fuel quantity then enabled the pumps to prime and we were able to use all the fuel on the next sector.

Airbus produced a document (I'll try to find it) about "wet & dry sensors" in the centre tank & an "over run timing logic" to control the pumps. If the centre tank pump switches are left on during refuelling, the pumps receive a continuous "run" signal (even when the tank is dry). This will bring on the low pressure warnings (after a short time delay) and may cause the pumps to loose their self priming ability.

After refuelling and the centre tank pumps are turned on again, the timer circuit prevents the pumps from running dry before the low pressure warning is given.

[dream747]

Goldenrivett,

This issue is still very common among our older MSNs, although I occasionally come across this happening on the newer frames as well. However, the FCOM procedure of switching the fuel pump controls to MAN and turning and the Center Tank Pumps off doesn't quite tell us when we can or should put them on again. So we turn them on after the refuelling is complete and we commonly see this issue when on days the center tank is only up to about 200kgs full, only to realise we may have 200 kgs of unusable fuel if it doesn't work after engine start.

Would be great to be able to have a look at that document!