Some advice about fuel contamination (Water)

[BlurE]

Hi guys looking for some advice - as after many years of checking fuel - last night I actually did find a problem. 

 

Some background first.

 

Not sure of the source of contamination, but I was away a few weeks ago and had to leave my aircraft tied down in some moderately heavy rain. I also flew through a number of light showers and refilled a couple of times including from a new perfectly clean plastic jerry can. 

 

My aircraft has LH and RH fibreglass wing tanks. Each feeds through independent lines from the back of the wing root through two taps before combining. There is a common drain point at the bottom of the fuselage and gascolator on the firewall.  Return line to the LH tank. The tanks do not have sump valves, so all I can really check is the gascolator and therefore which ever tank is switched on. I can switch on both tanks but then they cross-feed (meaning the levels I have off the dipstick are no longer correct) 

 

Before flying I always took a sample, but it has occurred to me that I was parked on a hill so water could have been trapped away from the tank outlets when I took samples.

 

Anyway I went to fly last night and open the opposite valve to the one I last few on. I collected about a two teaspoons (20ml) of water with a little bit of fine brown sediment.  Before this my samples have always been perfectly clear (yellow 95 RON)  I shook the sample and it formed spheres before resettling in the bottom of the glass.  (sorry about the blury photo - some irony there..)

 

I then took about another 500mL with no further contamination.

 

So maybe this has all the water out. But I think I drain both tanks and the fuel lines as completely as I can - and continue checking.

 

I might drain each wing separately and jack the aircraft so the port is at the lowest point.   I think i'll all so drain from the gascolator until dry

 

Funny thing is fuel checks were drummed into me throughout my training and early flying - but never with any real advice about an acceptable threshold or steps for rectification.  

 

Any other thoughts or ideas appreciated.

 

Cheers

 

 

 

[Head in the clouds]

Water can get into your tanks from a number of sources.

 

If you don't keep your tanks full, condensation can form on the inside top of the tank overnight and end up as a few drops of water found during your next tank drain check.

 

Always do your drain check on level ground, move the plane if required.

 

Always rock the wings before doing your drain check, that will help any droplets to move to the very lowest point where the drain is, and it will also dislodge any droplets that may be hanging on the top surface of the tank - ones which came about from condensation.

 

There's really no need to be overly concerned and drain your tanks completely, that's what your fuel drain check is for (to remove any water that has accumulated), don't forget that the fuel pickup point is above the tank sump where the drain check is done from. Also - the very reason for having a gascolator is to trap any water that might have been missed during the drain check, or which has accumulated since, by condensation.

 

If you drain all your fuel out, you may then be certain that there's no water in the tank, BUT tomorrow there may again be water in the tank, from tonight's condensation, so it's not a case of getting rid of all the water forever, it's a case of constantly removing whatever water might have accumulated for whatever reason.

 

Water can also get in through tank vents, tank fuel filler points and I had an interesting experience where more than 2 litres got in the tank overnight during heavy rain, it took a while to find the culprit, the flexible plastic/rubber tubing of the tank vent line had developed an almost invisible vertical split which allowed water running down that tube to enter the tank freely - that was on a Drifter with external tank and breather line.

 

 

[BlurE]

OK, sounds like I am overreacting a little, just something I had never actually seen before. Not a bad thing to be a little cautious.  

 

I suppose given that the inlet and outlet of the gascolator are at the same level you would actually have to pretty much fill the gascolator bowl with water before any substantial amount actually went up to the carburettors.  (assuming the flow rate is slow enough to allow separation) 

 

In this case I actually flew two turbulent hours between my last refuel and this sample that concerned me. Also a week of settling time in between.  So I suppose it's possible this little amount of water has been in the system some time but only recently worked it's way to the bottom.

 

 

[facthunter]

 It really relates to how your fuel pickup points are designed. If they are such that they don't drain from a defined low point, it's likely some water will be there constantly and only when agitated will some go into the gascolator.  You want the wings level and both tanks selected and rock the wings, wait a little while and perform the drain. If you are concerned repeat till no water is  evident. In fact that's the required procedure.. There's no harm in being careful. Nev

 

 

[Nobody]

The FAA have this fairly useful AC on water in Fuel. It does cover both Jet and Avgas so not all of it is applicable to our aircraft.

 

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC20-125.pdf

 

 

[facthunter]

 That's quite old stuff and there may be more appropriate info about.. There's a bit of a risk "all" of what you drain may be water and unless you run some on your hands and smell and feel it or use a TEST strip or Paste you might just get fooled. if you are in a hurry.. All inline filters should be frequently checked as well as the Carburetter bowl at least annually. Water with aluminium produces a white deposit that can interfere with the float action and block fine passages in the pumps or carburetters. Also there's the risk of galvanic action between dissimilar metals like brass and aluminium, gauze screens etc. Nev