Condensed Water in Fuel

[Capitan Morgan]

Hi @ll!

I hope, that somebody of the community may answer my question:
"Under wich circumstances do you expect the building of condensed water in the fuel tanks?"

I would be happy if you can explain me te conditions and details about building condensed water in the fuel tanks of an aircraft. When it may occur and when not?

Expecting to read your answers.

Regards
Capitan Morgan

[ShyTorque]

Condensed water in fuel? Anytime there is humid ambient air and a space in the tank above the fuel for it to be drawn in, where water vapour may condense into liquid form. That's why it's preferable to keep the aircraft tanks full when it's on the ground - there's less space for humid air in the tank.

Or someone might pump liquid water in from elsewhere because they didn't do a water check on the bowser.

On the other hand, if you find condensed milk in there, it's certain that some cow has it in for you. :E

.. is that last retort copyrighted .. or can I use it from time to time ? ... still laughing ..

[oldebloke]

As he says whenever there's space in the tank moisture,whether it's in the fuel or ambient air will condense on the surfaces of the tank.Cool the above and one gets ice.
This ice collects in the tank,and gels together..If you don't land in a suitable area(above zero)for a long enough time the Iceberg compounds.....
That is why Canada's principle airline(in the days of the 8')used to overnight the aircraft, to warm up the fuel in the Caribean,to eradicate estimated 500lb bergs...:ok:

[numbskull]

water condenses in fuel in the manner stated in above posts. However 747 and 767(and I must assume other A/C) have a small pickup at each fuel tank boost pump. It uses venturi effect to continually suck up small amounts of fuel and or water from the very bottom of the tank and deposits it at the inlet of the pump and gets used.

Therefore you will never find water in the tank after an A/C has landed but you may find 50-100 mils after the A/C has been on the ground for a day or so. Obviously the amount of water varies with the conditions.

[CaptainSandL]

I have never knowingly had water in fuel tanks but a colleague of mine had a (temporary) loss of thrust on an engine after take-off after collecting a 737 that had been on the ground for over a week in the UK for a repaint. I was collecting the next one and was given an engine run up procedure by Boeing to ensure that any water had been drawn through the lines before we got airborne.

On another occasion when I was waiting for a paint job to finish I got talking to a 737 crew who ferry aircraft all over the world. I mentioned the issue and they said that they had never experienced it and they had picked up aircraft that had been in storage in the desert for over 2 years! Maybe it is a local climate thing or maybe they drain off any water after long term storage.

S&L

[Blacksheep]

Contamination of fuel storage tanks and delivery systems is the main source of water in the fuel tanks of large transport aircraft.

Fuel quantity indication system defects are often caused by contamination of the fuel. I would always start trouble-shooting by taking a drain sample and checking it for water contamination. In the most extreme case I ever experienced, after refuelling an RAF VC10 there was a discrepancy of about 5,000 pounds between the bowser uplift and the aircraft gauges. I asked the refueller if they had done a drain check after refuelling and he said it was "clear and sweet" I double checked and it was indeed clear. An S.G. check on the sample however, showed an S.G. above point 95 - it was clear water, and almost drinkable! We drained two 40 gallon drums out of one inboard tank before getting a clear, clean fuel sample. I very much doubt if that nearly 80 Gallons of water came from condensation on the tank walls.

[Milt]

numbskull

I hope All of my booster pumps take in fuel from as close to the bottom of the tanks as possible just as my car does.

Some tanks even have sumps to ensure a bottom take-up.

Squash plate high pressure fuel pumps hate water with a vengeance. They must have continuing lubricity.

Special fuel additives are generally successful at absorbing small amounts of water in solution with the fuel and combat the formation of ice crystals if the fuel should reach very low temperatures. Fuel in the tanks is a large reservoir of heat and rarely is extremely low fuel temperature a problem even within integral tanks.

Fuel filters trap ice crytals and some can seperate out water.

[CV880]

In the B707/DC8 era, neither of which had scavenge jetpumps to pick up water in the tank sump area, many operators used to drain a sample from each tank sump drain valve into a bottle (one for each tank) and test each sample for water with the F/E witnessing the test before departure. An operator I worked for back in the 60's regularly found large uplifts of water in their DC8's after refuelling at Honolulu as the fuel in the tank farm at HNL (a hot humid place) was being consumed so fast it did not have enough storage time to allow the water to settle before being used. On arrival at our colder main base after a 9 hour flight large amounts of water could be drained out after thawing. In fact the outboard engines suffered fuel filter icing as the freezing of all this water overwhelmed the fuel heaters and Douglas had to come up with a mod to improve the fuel heater efficiency (outboard engines fed from outer tanks which got colder than inner tanks).
Early 747's did not have a scavenge jetpump system and had a significant problem with the very large No. 2 and 3 main tanks accumulating huge amounts of water that affected the quantity indicating system (water contamination of the innermost probes, densitometer etc).

[DaveySimon]

I'm pretty sure no-one mentioned that warm temperatures will increase the potential of water forming in a fuel tank.

[numbskull]

Milt,thanks for the lesson in fuel systems. In a 767/747 there will always be around 100kg/litres of unuseable fuel or more after the boost pumps run dry and other large airliners would be the same.

Kerosene is very effective lubricant for the pump and it would have to be pumping 100% water for some time to effect the low pressure boost pumps in the tank.

Fuel would also go through at least 1 fuel/oil heat exchanger on any modern airline engine which along with cooling the oil ,heats the fuel to to assist in atomistion of fuel in the combustion chamber and eliminate any problems of icing in the fuel.

I work in a warm environment but I am not aware of any problems from water condesation that modern fuel systems in airliners combined with regular fuel drain checks by maintenance won't overcome. The only problems I have heard of is fuel that has been contaminated by water prior to uplift to the aircraft which is a different issue.

Milt what Aircraft has fuel filters that seperate water?? There are many air filters that seperate water but I haven't heard of a fuel filter.How does it work???

[jettison valve]

With my (limited) experience, I would say the A340-600 is the worst aircraft type when it comes to water accumulation in fuel tanks; we call it the fuel-to-water-converter:
You take out gallons of water every other day, and the recent incidents concerning the ruptured engine feed pipes are very likely linked to frozen (!) thermal relief valves (no, they are not located in the sump areas!!!).
It appears that Mr. B´s design to feed water from the sumps into the boost pump areas is superior to Mr. A´s water "mixing" philosophy.

Long live the A340-500/600, the job-saving aeroplane! ;-)
J.V.