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**Mark Goldberg** · 11-11-2016, 08:46 PM

I like Pro Seal for this kind of repair. On my RV8 leading edge tanks built up with Pro Seal, it was used over screw heads and things very similar to those rivet heads.

Just one thing I will mention after talking to Dennis, the husband of Donna who made this post. Interestingly, they leak tested the tanks by pressurizing with air and placing a balloon on it. The balloon was still blown up the next morning. It is hard to imagine that any leak at all would not let the air out over night. But it didn't. Must be very, very small leaks it would seem. Mark

**corefile** · 11-12-2016, 11:34 AM

Originally posted by Flygirl1

Well I found two more teeny tiny leaks in one tank this morning. (One of the guys says having a "teeny tiny" fuel leak is like being a "little bit" pregnant. LOL ) So as far as welding, which ones do you weld. If I put another 15 gal. in will the weight cause more over time? Who knows, so I still think pro-seal is the way to go. Fortunatly these wings have really good inspection panels to keep an eye on things!! Mark G. thanks for your thoughts and your offer to help. Really appreciate that. If pro-seal doesn't work, I'll give a shout. Donna

Sounds like you have 4 or more spots where you have fuel seeping around rivets? If it was me I would pull them and ask Marc for an exchange - just asking for trouble going forward.

Marc - as you mentioned you have shipped hundreds of tanks with no problems before - so not giving you grief - just a curiosity point for me, how are they testing the tanks at the factory?

-paul

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**Pat Fagan** · 11-12-2016, 10:04 PM

I have had good luck with the fuel tank repair compound sold at auto parts stores. Slice off a small piece of the stick, roll it between your fingers to activate it then mash it over the rivet. Inexpensive and a lot less messy than proseal.

**Mark Goldberg** · 11-13-2016, 10:40 AM

I am waiting for someone smarter than me to explain how Dennis did the balloon pressure test with the balloon staying blown up over night - and then subsequently finding these small leaks. That doesn't make sense to me. It would seem air would escape from ANY leak, however small. Someone enlighten me how this could happen. Mark

**Battson** · 11-13-2016, 03:25 PM

I have to say the balloon test didn't work for me either. My test showed no leaks on my fuel system, but when I added fuel I found almost all my joints were not tight enough. I can't say why the test doesn't work well, but I can corroborate that the balloon test is fallible.

**JimParker256** · 11-13-2016, 03:29 PM

I'm certainly no expert on this topic, but I read on one of the other airplane building forums (can't remember which one now) that "pressure testing" of fuel tanks is a good way to cause fuel leaks, as the metal responds to the internal pressure by bowing outward, which can actually create the leaks - especially around rivet heads. Their suggestion was to plug all the drain points, cover the tanks with a thin film of talcum powder, then just fill the tanks with water, and look for leaks overnight. I have no idea if this is "sound" or not - just reporting what I read elsewhere...

**Mark Moyle** · 11-13-2016, 05:37 PM

Comparing gasoline to water...gas has zero surface tension compared to water. Picture in your mind Tyler 2000 mesh screen...doesn't exist but imagine how small the openings are. A screen that small will hold water simply because of surface tension. Gasoline goes right through it even though the size of the gasoline molecule is like comparing Jupiter to the moon.

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**BTAZ** · 11-13-2016, 05:39 PM

When I welded up my tanks, the last few leaks I chased down were small enough that the balloon didn't seem to change even after 8 hours(apply balloon in the PM when I closed up shop, checked when I left for work in the AM with no apparent visual change, check when returning from work and balloon was very slightly smaller.) I was ready to attribute it to changes in barometric pressure but very careful work with soapy water revealed what I hope are the last ones. Note I haven't put fuel in yet so for all I know there may still be leaks. Perhaps if one was a bit more scientific(put a couple marker marks on opposite sides of the balloon and use a flexible tape to measure/track the distance as opposed to "Does it look smaller?") might pick up the leak quicker.

My IA friend doesn't believe in testing tanks with water in that in his experience he has seen leaks which are small enough to pass gasoline but not water. There is filter media that proves this out(http://www.twpinc.com/wire-mesh-by-p...uel-from-water)

A leak from a rivet as described I personally would be fairly comfortable fixing with epoxy as it isn't likely to grow. A leak from a seam I would want welded as I could see a hard landing or turbulence causing the crack to "zip open", traveling along the seam out from under the epoxy with unpleasant results.

My experience with other fuel tanks outside of aviation (cars, tractors, motorcycles, etc.) is that both JB Weld and the "Fuel tank repair epoxy" make for long lasting repairs but the JB Weld approach requires the tank to be empty and the leak free of gasoline or it won't stick.

But my IA friend would insist on Pro Seal for an aviation tank on an experimental.

**Mark Goldberg** · 11-13-2016, 07:05 PM

I just heard from Donna that they probably did not do a balloon test on the tanks. Just on the fuel system itself.

I also spoke with Bob Barrows about this. He said that over the years he has had a LOT of fuel tank leaks. He has repaired most of them with JB Weld and that has worked well for him. However, I still feel ProSeal is the best choice since it is made just for sealing tanks. Messy to use but a very good product for what it does. Mark

**OhioLSA** · 11-13-2016, 08:40 PM

I was preparing to do the balloon test on my tanks, but now I'm thinking it might be worthwhile to simply fill them with gasoline (since that's what they're supposed to hold) and see if they leak. Sure, it's somewhat of a hassle to then have to drain the gas into other containers, but it might be an effective test.

**BTAZ** · 11-13-2016, 08:56 PM

I would start with the balloon test. Fix all the leaks you find by welding when it is a much easier(and safer) task without gasoline fumes to worry about.

My experience is that "the balloon" will find some pretty small leaks if you are patient and somewhat scientific in your approach. When I completed my leak chasing on the tanks I built, the balloon remained unchanged after 24 hours whereas the "last leak detected" had a visible impact on the balloon size after sixteen hours or so.

My plan is that if I find some leaks when I have already put fuel in the tanks I built, I will likely address them with JB Weld (or Devcon) or Pro Seal

**Bdflies** · 11-13-2016, 10:10 PM

Reading this thread is starting to spook me! Both tanks are mounted in my wings, but not hooked up or plumbed. I could remove them, blug all the bungs and fill them up or pressure test them. Re welding leaky rivets wouldn't be too hard at that point. It would be even easier (at this point), to just scuff the welds, clean them with MEK and apply a nice dollop of JB Weld on each rivet. I can think of several reasons to do this "prophylactic" fix and am hard pressed to think of a reason not to. So, what y'all think?

Bill

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