Fuel Tank Leak?

[JoeRuscito]

It seems I may have a tank leak. Now that my wings are complete I figured Id pressure test the tanks again with all of the fittings/sight tubes installed. I first tested them connected together at the main fuel supply ports and plugged the air vent line (with a plugged tycoon tube) and fuel caps (with sealing tape). I blew into the tanks enough to get the tape to bubble. I found this configuration leaked enough that the tape wasn't bubbled after about 12 hours. Then I separated the tanks to test individually. They both hold lung pressure for about 24 hrs before I can no longer see the tape is bubbled. So both tanks seems to leak at about the same rate and quite slow.

Im wondering if I should be concerned or if this is what others have observed. Im wondering if the quick drain might leak air but not fuel. Or if the tanks should hold air indefinitely and I need to go searching for leaks at each of the fittings.

Thanks for the help!

[jrevens]

Hi Joe,

It’s difficult to seal the filler openings with tape to make a perfectly air-tight seal. I found that aluminum duct tape worked best for me. So... you may or may not have leaks in the system. You can use a soapy water solution in a spray bottle to leak check, looking for tiny (or not so tiny) bubbles forming. If you have good seals on your filler caps you can connect balloons to the vent tubes as a pressure indicator also. Regarding the quick drain valves - if they leak air they leak fuel.

[JoeRuscito]

Well it was the main pickup line. The fitting was leaking at the threads where the finger strained threaded into the tank. After talking to the factory my only option was to cut the elbow to unscrew and redo the sealant.

For anyone out there that doesn’t have the banjo fittings. Get them. It would have been a simple fix if they were installed.

Also, my suggestion would be to leak test the tanks for a second time just before covering and with all of the fittings installed. Just my two cents.


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[Shadowrider]

So you just removed fitting and it needed more sealant?

[JoeRuscito]

Yes. And also I may not have tightened enough. I was pretty conservative in tightening so as to not crack the tank. So when the elbow was level and what I thought was tight enough I stopped. Rather than going for a whole additional rotation of the strainer and risking cracking the tank. I hope that makes sense.

[Shadowrider]

Yes thanks. Crossing my fingers for no leaks. I did test mine after installing fittings but not overnight.

[JoeRuscito]

I have two successfully tested tanks! Both held air while connected together for 24+ hours. I think Im good to go. Retrofitting for the banjo fittings was a bit of a project but got it done... highly highly suggest doing this from the start... Also the new sealant the factory is shipping, its blue, Needs to be added to both threads male and female to form a tight seal and before inserting needs to sit for quite a while (read 30 mins or so) for the solvents to evaporate. I originally only put the sealant on the male threads and avoided the last thread with the thinking this would keep from contaminating the tank/fuel... it seems for this stuff to work that thinking needs to be abandoned.

Just my experience in case it helps anyone.

[jiott]

Putting it on both threads sounds very bad to me; you will just push it off the female threads into the system-not good at all. Those instructions I believe are for when you use it to seal two flange surfaces. I would NEVER NEVER do that on a fuel fitting. One of the common causes of fuel system failure is pieces of teflon tape or other sealants in the fuel system causing blockages. This is very serious. Please call the factory and ask what they recommend for proper procedure with this new thread sealant they provide, then let us all know.

[JoeRuscito]

That was also my original thinking! I will call to clarify once again...



Putting it on both threads sounds very bad to me; you will just push it off the female threads into the system-not good at all. Those instructions I believe are for when you use it to seal two flange surfaces. I would NEVER NEVER do that on a fuel fitting...

[JoeRuscito]

...from the factory... "Yes we are using the new sealant and yes you should be fine.. You installed according to the directions.

You will get sealant residual in the system and therefore a good practice is to clean the inline filters after about 10 hours of operation… Also be sure to sump the header tank.. especially the first fuel runs.. "

[Danzer1]

...from the factory... "Yes we are using the new sealant and yes you should be fine.. You installed according to the directions.

You will get sealant residual in the system and therefore a good practice is to clean the inline filters after about 10 hours of operation… Also be sure to sump the header tank.. especially the first fuel runs.. "

WOW is all I can say to that! Out of curiosity what brand is this new blue goo? Likely solvent based if it needs to sit open. If so, some are not compatible with alcohol (ethanol). I'd do some research.

YMMV, Greg

[jiott]

I also say WOW! What if someone uses it that way on a fuel fitting downstream of the last filter. The residual could easily clog up the very small jets and orifices in the carburetors. Its been awhile since I read thru the FAA publication on recommended practices for aircraft construction and maintenance, but I believe pushing sealant into the fuel system is totally against their directions.

The stuff Kitfox recommends is Permatex Permashield 85420 Gasket Dressing and Sealant. When you read the application directions it says nothing about threads, but talks only about gasket and flange surfaces. It is specified as being fuel, ethanol resistant.

Personally, I will continue to use it by applying to the male thread only and leaving the last couple of threads bare.

[efwd]

If I may add my 2 cents worth. I didn't deliberately place this sealant to the tank threads first but I did apply it to the fitting threads and installed it. I found that I was not holding air in the tank via the balloon on the cap vent tube. I removed and reinstalled the fitting about three times, each time I reapplied the sealant to the male threads. By then I had residual sealant on the tank threads and it did end up sealing up. I fully expected to find debris within the fuel system and as I have stated before the only stuff I found (still finding it a bit) was the little white granuals that resemble sand. Because of this finding during fuel samples, I have removed the large fuel filter and cut it open. I found absolutely nothing in that filter. I think at the 100 hr I will change the inline filter I have coming off the header tank. I suspect that that is where all the debris might be. Either that or the sump drains are doing a fine job at capturing it and Im purging it on fuel sampling.

[jrevens]

Interesting. My instructions specifically specified Permatex 80938 (9AR) for this. I recently had to remove one of my tank quick drains and asked John at Kitfox what they now used. He said it was the 9AR. It is creamy white in color as opposed to the blue 85420 you guys are talking about. I think that the 9AR has possibly been discontinued by Permatex, but I was able to get a new tube on Amazon, at a ridiculously high price. Threading and sealing a metal fitting directly into a tapped fiberglass hole is potentially problematic, and there should be a better way. If I was starting over, I believe I'd drill and tap the tanks oversize, then bond brass threaded reducer bushings into the tanks with a structural epoxy. A metal to metal joint on fittings that may have to be removed would be a much better design, IMHO. Better still would be to redesign the tanks slightly to allow that to be done while also providing additional clearance to better accommodate the metallic bushings.

[JoeRuscito]

Guys I really appreciate all of the input, not that I feel any better about the situation as a whole... I think I will simply have to diligently check the filters through the first hours. Maybe to some extra time running on the ground before any flight takes place. My wonder remains, will everything that might release, release in the first few hours... or might I have a nasty surprise many hours down the line. I may scope the inside of the tanks/header tank with a camera just to see how much is in there...

[jiott]

I built my whole kit using 9AR on every tapered threaded fitting including fuel, brakes, oil and coolant and have had zero leaks for 740 hours; I like the stuff. However I recently used it up and bought the blue 85420 which I have not used yet. My understanding was the 9AR is no longer available and Kitfox factory has been selling the 85420. I always used the 9AR by putting it only on the male thread, but don't remember what the actual instructions on the tube said. I believe the 9AR was also described as a gasket/flange sealant rather than a thread sealant.

I understand from this forum that many folks have been using Loctite thread sealants on their projects with apparently good results (those thread sealants instruct you to apply only to the male thread). My own hesitation in using them is that they cure to a hard non-flexible condition which is fine for metal to metal fittings torqued to proper tightness. But for a metal fitting into fiberglass where the torque value is extremely low I want the non-hardening sealant that remains flexible and of course is compatible with ethanol containing fuel. My 2 cents.

[Flying Felix]

Hello everyone,

Have you thought of researching Hylomar Universal Blue? It does not harden and it works well with various fuels. Might be worthwhile to look into it.

Happy flying!

Flying Felix

[Dave S]

Per John's comments - exactly what I found to be true.

Permatex 9AR was re-branded Permatex Tack & Seal Gasket Sealant Item # 80938; and, the tube clearly has 9AR in parentheses following the Item number 80938.

It's the same stuff; or, similar enough to be indistinguishable in physical characteristics or uses.

Business just loves to rebrand stuff.






Interesting. My instructions specifically specified Permatex 80938 (9AR) for this. I recently had to remove one of my tank quick drains and asked John at Kitfox what they now used. He said it was the 9AR. It is creamy white in color as opposed to the blue 85420 you guys are talking about. I think that the 9AR has possibly been discontinued by Permatex, but I was able to get a new tube on Amazon, at a ridiculously high price. Threading and sealing a metal fitting directly into a tapped fiberglass hole is potentially problematic, and there should be a better way. If I was starting over, I believe I'd drill and tap the tanks oversize, then bond brass threaded reducer bushings into the tanks with a structural epoxy. A metal to metal joint on fittings that may have to be removed would be a much better design, IMHO. Better still would be to redesign the tanks slightly to allow that to be done while also providing additional clearance to better accommodate the metallic bushings.

[JoeRuscito]

WOW is all I can say to that! Out of curiosity what brand is this new blue goo? Likely solvent based if it needs to sit open. If so, some are not compatible with alcohol (ethanol). I'd do some research.

YMMV, Greg

This is the blue goo in question:

https://www.amazon.com/Permatex-PermaShield-Resistant-Dressing-Sealant/dp/B01M164DO0/ref=asc_df_B01M164DO0/?tag=hyprod-20&linkCode=df0&hvadid=312061076118&hvpos=1o2&hvnetw=g&hvrand=14503524908538953574&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1025521&hvtargid=pla-585235998177&psc=1&tag=&ref=&adgrpid=62430536632&hvpone=&hvptwo=&hvadid=312061076118&hvpos=1o2&hvnetw=g&hvrand=14503524908538953574&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1025521&hvtargid=pla-585235998177

It does state that it is resistant to ethanol.

[Maverick]

Would someone describe what the banjo fittings are or show a picture of these. I'm not familiar with this term.

[PapuaPilot]

Here is a picture

https://www.aircraftspruce.com/cache/370-320-/catalog/graphics/5/05-06473.jpg

[JoeRuscito]

This blue stuff needs to go.... used the same stuff on my brake fittings and now those are leaking.

I think Im going to redo every fitting on the plane with the re branded 9AR stuff "Permatex 9AR was re-branded Permatex Tack & Seal Gasket Sealant Item # 80938"

So any ideas on good ways to clean the blue stuff off. It leaves quite the mess?

[efwd]

MEK. My brake line fittings wouldn't seal with the blue stuff either. Fuel Lube that I bought at AS&S worked.

[bbs428]

EZ Turn is the sealant I have been using.

"A specialty lubricant/sealant used for fuel and oil line valves & is resistant to high temps. Especially effective where high octane fuels and aromatics are present. EZ Turn is also extremely efficient as a gasket paste & anti-seize agent. EZ Turn will not gum, crack or dry out. Each shipment is independently tested. Excellent for tapered plug valves, aircraft engine manufacturing, and marine applications."

E-Z Turn Specification Sheet:SAE-AMS-G-6032MIL-G-6032D Am I Type I

Dropping Point 9126.7°C min.) >600°F ASTM D-2265
Unworked Penetration 260 ASTM D-1403
Worked Penetration 220 ASTM D-1403NLGI Number 3 NLGI
Consistency Soft VisualColor Cream Visual
Resistance to Aqueous Solutions - Distilled Water Pass; no deterioration FTM-5415
Resistance to Aqueous Solutions - Ethanol:Water50:50 mixPass; no deterioration
FTM-5415Resistance to Fuel/Appearance Pass
FTM-5414Fuel Solubility (20% max.) 1.11%
FTM-5414Water Spray Off 2.33% ASTM D-4049
Water Washout at 175°F (Bearing Dried at 77°C) 6.63% ASTM D-1264
Load Wear Index 74.09 ASTM D-2596
Load Wear Index (Last Non-Seizure [Scar]) 160kg (0.48 mm) ASTM D-2596
Load Wear Index (Last Seizure [scar]) 200 kg (0.71 mm) ASTM D-2596
Load Wear Index (Weld Load) 250 kg ASTM D-2596
Copper Corrosion (#1b max.) Shiny 1b FTM-5309
Film Stability and Corrosion on Steel Pass; no corrosion ¶4.6.3
Roll Stability - Original Penetration 271 ASTM D-1831
Roll Stability - After Rolling Penetration 275 ASTM D-1831
Roll Stability - Change in Penetration +4 ASTM D-1831
Roll Stability - Percent Change +1.48% ASTM D-1831
EMCOR Rust Test, Bearing A #4 ASTM D-6138
EMCOR Rust Test, Bearing B #5 ASTM D-6138
Dielectric Strength 112 volts/mil ASTM D-149
Breakdown Voltage 5,597 volts ASTM D-149
Dissipation Factor @ 1 kHz/73°F/50%R.H. 0.0782 ASTM D-150
Dielectric Constant 5.95 ASTM D-150
Low Temperature Torque at 0° F - Starting Torque 55,250 g-cm ASTM D-1478
Low Temperature Torque at 0° F - 1 Hour Run

Passed all the leak down tests. I did tighten my fittings down very well. I used the same procedure as Jiott and others. I will do the test again before covering and consider the Banjo fittings. Thanks for the heads up.

23016

[efwd]

Yeah, that's the stuff I thought was called Fuel Lube. That is what pops up when you put Fuel Lube in the search box on AS&S site. It works great for sticking washers to the nut when you cant keep the washer in place long enough to get a nut on the bolt. You know, those really tight spots.