A320 CTR TK pumps and slats.

[ahmed88]

whats the relation between those ? when slats are extended the center tank pumps go off, when retracted they go back on. this rule is ignored for 2 mins when an engines starts.

WHY ?

[Reimers]

but rather used as an easy thing to determine that the aircraft is manoevering close to the ground. They want the engines to be fed directly from the wing tanks and gravity feeding to be possible should the pumps fail.

[ahmed88]

but the wing pumps are already running all the time, except that when the center ones are 'on' the wing pumps deliver less press (sequence valve), so if the center pumps failed, the wing pumps should take over immediately. for me it seems more redundant to have the center pumps running on whatever config.

thanks for the reply.

[FaHaD_7arB]

it will run for 2 min. as scavenge pumps during eng. start
after that, they will go off due to the load shedding

[hawkeyecheck]

Sequence valve in incorporated only on wing tank pumps so that the fuel is first fed from center tank and then the wing tanks . but when slats deployed its fed from its individual wing tanks....i do agree with remiers on this. After take off slats retracted in cruise mode again it will fed sequentially from center tank if present till low qty is triggered and pump gets off. SEE AMM or Fcom for more details....:)

[King Khan]

Ahmed, what you asked is a very good question. The Design logic in A320 is that the fuel is fed to engines from CTR tank first then the Wing tanks but when Slats are down, it is normally Take Off Config and we don't want any problem in fuel feed to engines during this time in case CTR tank pumps block/fail and so Wing tank pumps run with slats down because Gravity feed is possible from Wing Tank pumps should they fail.
And irrespective of slat position during engine start the CTR tank pumps runs for 2 mins because it is just to clear out the Water in the fuel tank bottom before the a/c enters the crucial phases, Actually burning away the water with fuel in the very beginning....
Just thought of sharing my knowledge though its too long since you asked this but may help other brothers... Peace....

[Bite OK]

i would like to add some points i have gained from my type course:

presueming a/c tanks are full, during engine start CTR pumps runs for 2 min thats to check the pumps runs properly and then stops, at this time during taxing the design logic to burn some fuel from wing tanks to give some space for fuel cooling circulation coming from engine Fuel/oil heat exchangers ( cfm & V2500 OIL COOLING SYSTEM).

on cruise phase CTR tanks supply fuel and empties first, this to keep wing tanks with fuel for long as possible, reduce wing structure loads.

just some addition to previouse post

regards