Ollie I have understood this and how the deaerated fuel works and so on. Your answer covers the first question about FL150 and thanks for that. The main issue was the sequence of events because I haven't seen the actual failure in the sim, so I have to visualize it. I slept in the night thinking about it and I have found some answers. For the sake of the conversation I will go will the visualization process.You are climbing, at FL200 you have an ECAM for Left tank pumps low pressure. The procedure states, xfeed on and pumps off. So you do that, you make a fordec and you say I have the fuel to continue to my destination because it's tankering, so I can easily climb at FL350 stay there for 30 minutes and still have plenty of fuel in the right hand side of the wing. So you do that.
The procedure states, that WHEN FUEL OF THE AFFECTED WING NEEDED go for the gravity fuel feeding procedure. So you open the QRH and you do the checklist. You put the XFEED OFF because it states when reaching gravity fuel feed ceiling put it off, so at that moment the right hand engine is taking fuel from the right hand from the pumps, the center tank is empty and the left hand engine (the one without pumps) takes fuel through gravity forces so it continue to run.
Then, you go to the next line which says, If no fuel leak and with one engine running (fed by gravity) - which is our case - :
xfeed on, bank angle .. 1degree wing down on the live eng side - this is the right side on our example -
rudder trim ... use.
So bottom, line both of your engines continue to run since both are supplied with fuel somehow. If the left tank depletes a lot you may lose the left hand engine on the approach in case you dont or you cant open the xfeed again.
Am I correct?
Now the questions for the things that aren't clear to me.
1) This sentence: If no fuel leak and with one engine running (fed by gravity), assumes that you may have have 1 engine live (fuel pumps working) and the other fed by gravity - so in general 2 engines working, which is our case - or scenario 2, no engine working through the fuel pumps and you have to make one engine working through the gravity feeding process correct? Like if in cruise you put all pumps off, at some point the engines will go off. Assuming you dont put them on again, you have to bank 1 degree to the right to make your left hand engine take fuel by the left hand side, but this means your right hand engine will not have enough pressure and gravity to take fuel from the right hand side, so this engine will remain off. Do I get it correct?
2) Also, the FCOM/QRH has a gray zone about the deaeration of the fuel. If you search by your own, you know why the limitations are there, you learn about Henry's law and etc. But it doesn't specify at any point if the deaeration needs the fuel pumps to work in order for it to happen or not. So, this is a process that happens once the pumps are working on take off because the initial force has been given and it continues by itself OR you need the fuel pumps to work in order for the pressure and all that to be supplied and the air to deaerate?