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Fuel tank leak along the tank inbd rib-fwd

Jskyking

Well Known Member
I have a Very small leak in one of my newly sealed fuel tanks. (Tank will decrease from 28” H2O and hold steady at 5” H2O on the water gauge.) This afternoon , I found the leak using Snoop in the corner of the TANK INBD RIB-Fwd where it adjoins the tank attach bracket assembly.

My plan is to thin some Proseal and try to spread it around the flange and the pull a very small vacuum on the tank. Lastly, I will scuff redcoat the area with full strength Proseal.

Two questions:
1. Is there a preferred thinning agent for Proseal? I’ve read that MEK or TOLUENE/toluol. With the latter being preferred. Curious if XLENOL would work also.

2. Pulling a vacuum: should I use a hand vac from the auto parts store and limit the vacuum to approximately 1 psi or can I use a suction tube and draw enough vacuum to weep the Proseal into the suspected area?

Thanks
 
Speaking from experience after having repaired leaky tanks, I suggest opening up the tank - as painful as it is, and getting it from the inside. It was simple to cut a hole in the rear baffle and use the kit that vans offers to seal it back up.
 
Dive in and do it right.

At the stage your at, I would go inside and do it right..If the -14 tank is similar to others, at least you can get in through the sender/pick-up access. If it were a flying/painted plane, I would try the other method mentioned. At my day job (maintaining KC10's, the largest flying gas station), we would draw negative pressure and locally inject 1422A sealant, thinned with MEK if needed in the event we needed quick fix for a leaking tank. The "A" is brushable thin Proseal, rather than the usual "B" sealant RV tanks are sealed with. When I built my -4, after I completed the tank seal/close, I brush coated the entire outer rivet lines and joints with the "A" sealant.
 
Contd fuel tank leak scenario

Thanks for the ideas. I should have attached the pictures of the affected area. The location would present a sporty scenario as the bracket assembly blocks easy access as illustrated in the attached pictures.
Yesterday, I spoke with Vans- they said due to the location, they would try an external repair first then if that didn’t work, then go with the access method. The thought of removing the sender was discussed, but eliminated due to lack of working room behind the bracket assembly. They also said I have about a 60/40 chance that it will hold. If it does hold then the repair should last forever.
I’m leaning towards thinned Proseal and vacuum, as I can always fall back on opening the rear baffle with a repair kit.

Lastly, I removed the water gauge and put it on the other wing where I had a manometer. It started at 26in. H20 yesterday afternoon. Checking it this morning, overnight it dropped to 13.5in h20. The wing is in my shop which isn’t climate control, and the temperature dropped probably 10-15 degrees. I did an extensive snoop soap test, and found no evidence of leak. Is this drop normal?
 

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How did the repair go?

I'm curious which method you used for the repair and the results? After passing all of my previous pressure tests, I've developed a leak in the same place. Unfortunately, the wing all closed up and installed, though not yet painted.

Mark Easton
 
Mark , my wings weren’t installed so my method may not work without the tanks being off the wing. Anyhow, I used an automotive brake hand vacuum, I think it’s a Mity Vac. First I pressurized the tank with air as measured with a water gauge. Then used Snoop to positively identify the affected area. The whole was extremely small and difficult to find, but Snoop worked better than any other medium.
Once identified, I pulled the vacuum. It took a lot of pumping probably 10+ minutes, the skin make a very distinguished noise, that’s where I stopped. I put Snoop back on the area and Nothing....bubbles stayed static. Maybe, the Proseal found the leak thru the vacuum process- I really don’t know. As a precaution, I Reapplied Proseal to the flange area. I let the Proseal for about a week, then repressurized the tank. It held solid pressure as measured on the water gauge for over 10 days.
Had the above procedure not worked, I would have had to cut a hole in the rear baffle,to access the area and then blindly put Proseal on the inside.
When we were initially prosealing, we took great care to “ wet flay seal “ all the flanges and all of the nooks and crannies. I used approximately 1.25 qts of Proseal, so I wasn’t leaving anything to chance.

I also considered putting some AvGas in the tank, but didn’t do it. When I pressurized the tank, I dunked it in a wading pool to help isolate the leak then used Snoop to narrow the hunt.

All the Best
Jay
 
Thanks Jay,

Mine actually passed the leak tests prior to installation. My theory, at the moment, is that when lifting the wing from time to time, the forward tank attachment flange was used as a lifting point and it tweaked the proseal along the seam enough to cause a leak. In any case, I hope I can get it stopped without having to open her up.

Mark
 
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