Geeky AIRBUS question...A320 suction valves and jet pumps

[fidelio]

Hi

Does anyone know how many suction valves there are in each inner tank.. is it one or two? Similarly, do you know how many jet pumps (for newer aircraft) there are? I presumed there are two suction valves and one jet pump (for each side on newer aircraft) but unless I have totally missed it I can't find it in FCOM anywhere. FCOM just mentions that they exist without specifiying how many there are, as far as I can see.

Thanks

[tubby linton]

Have a look at this . It shows the A320 and A321 fuel systems
http://www.smartcockpit.com/download...For_Pilots.pdf

[Polorutz]

There are two electrical pumps for each inner wing tank. Also for each inner wing tank there is only one gravity feed.

Depending on the model, you can either have 2 center tank pumps or 2 jet pumps.

If there is a jet pump, what they do is transfer the fuel from the center tank to the inner wing tanks. If it's the older model they each go to an engine.

[fidelio]

Thanks guys.. so it appears that there are only two jet pumps (one for each side... same number as centre
Tank pumps in older models), and as for suction valves, the diagram on p100 of the PDF you kindly provided seems to suggest there is only one per inner tank (even though there are two pumps per inner tank). Makes gravity feeding much more precarious that I had thought I must admit.


Thanks

[Goldenrivett]

Makes gravity feeding much more precarious that I had thought I must admit.

How many times have you known gravity to fail?

[Peter G-W]

Every Friday night.

[Uplinker]

It doesn't fail on Friday night, it gets stronger !

They ususally keep it on at weekends though, which is nice.

[Escape Path]

Can't see the point in that. No wonder I keep falling when I'm drunk on the weekends

[capt.topgun]

Originally Posted by Polorutz

There are two electrical pumps for each inner wing tank. Also for each inner wing tank there is only one gravity feed.

Depending on the model, you can either have 2 center tank pumps or 2 jet pumps.

If there is a jet pump, what they do is transfer the fuel from the center tank to the inner wing tanks. If it's the older model they each go to an engine.

How is the fuel fed from Center tank by gravity (new Jet pump model)? Last 2T are unusable alright but how is the rest used in case of ELEC EMER? Is the Jet pump a mechanical pump or merely a suction creating mechanism?

[Goldenrivett]

Is the Jet pump .... merely a suction creating mechanism?

Yes.

http://www.eaton.com/ecm/idcplg?IdcS...Name=CT_207260

[capt.topgun]

Thanks for the detail.

How is the Jet pump able to maintain suction with the Inner Tank Pumps powerless in ELEC EMER? The suction is created by fuel running around the Jet Pump under pressure.

[Goldenrivett]

How is the Jet pump able to maintain suction

The engine fuel supply runs from the tanks through the "spar valve" (LP fuel valve) located on the wing front spar. The fuel supply then runs "downhill" through the pylon to the engine driven fuel pumps. When you are "gravity feeding", the lowest pressure in the fuel run is at the highest point which is near the spar valve (during cruise or climb). Fuel is being delivered through the plumbing because the engine driven fuel pumps create a lower pressure on the "suck" side. Provided the fuel remains liquid in the plumbing system then the engine will run happily. If the pressure gets too low anywhere in the plumbing and vapour (gaseous fuel) forms then the "syphon is broken". The mechanical fuel pump can't pump vapour efficiently and the engine is starved. Hence the published gravity feed ceilings (where atmospheric pressure is needed to stop the fuel forming vapour anywhere between the mechanical fuel pump and the fuel tank inlet).

Since the fuel is being "sucked" from the tanks (really atmospheric pressure pushing the fuel through the plumbing towards the low pressure at the mechanical pump entry) and the jet pump in the centre tank works in a similar way (pressure differential i.e. suck) then apparently some of the centre tank fuel can be extracted whilst gravity feeding.

See engine driven fuel pump: eaton fuel pump

Please see EASA warning Airworthiness Directive
AD No.: 2016-0205
Issued: 13 October 2016 google.co.uk.easa.europa.eu%2Fad%2F2016

"Reason:
Airbus introduced mod 154327 on A319 and A320 aeroplanes which substituted the pump fuel feed system from the centre fuel tank with a jet pump transfer system, based on the Airbus A321 design.

Subsequent investigation determined that ground wires had not been installed on the Fuel Level Sensing Control Units (FLSCU) of the modified A319 and A320 aeroplanes, due to a drawing error on the fuel system recirculation Principle Diagram. Without these ground wires providing inputs, the FLSCU logic is not correctly implemented for gravity feeding operation.
This condition, if not corrected, could lead to reduced fuel pressure at the engine inlet, possibly resulting in an uncommanded in-flight shut-down when flying at the gravity feed ceiling levels, as defined in the Aircraft Flight Manual (AFM)."