Bill3558 Posted October 14, 2022 Report Share Posted October 14, 2022 I had a slow leak, now I have a fast leak after I tried tightening the fuel line fitting into the header tank. Fuel seems to be coming from under the fitting. When I disconnect the fuel line, the fitting is loose and just spins. Shouldn’t it tighten up? any help appreciated since I can’t call FD till Monday. Quote Link to comment Share on other sites More sharing options...
Bill3558 Posted October 14, 2022 Author Report Share Posted October 14, 2022 By the way I was able to turn off the fuel by removing the fuel tank selector cover and turning it 180 degrees which is a fuel cutoff. Arian told me that little trick. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted October 14, 2022 Report Share Posted October 14, 2022 The fitting is a flared fitting. I have had to deal with a couple. I unscrew it and apply some blue Hylomar on the threads and the tapered tip of the male fitting. DO NOT get it into the fuel flow. Keep the tube opening clear of the Hylomar. Then screw it back down. I have never had another leak by doing this. Hylomar doesn't harden like glue. It stays soft and workable. Hylomar is also used on our fuel bulkhead plate up at the fuel sight tube. Quote Link to comment Share on other sites More sharing options...
Bill3558 Posted October 14, 2022 Author Report Share Posted October 14, 2022 Roger, i don’t think it’s the flare fitting that’s leaking. It’s leaking from underneath the fitting the flare fitting screws on to . Check out this video . IMG_0079.MOV Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted October 14, 2022 Report Share Posted October 14, 2022 As an A&P, I would consider Hylomar on a flared fitting unacceptable. If it doesn't seal as intended, something is wrong. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted October 15, 2022 Report Share Posted October 15, 2022 I've not had one of those plates off, but it could have a nut on the back side, and turning the fitting has broken the seal. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted October 15, 2022 Report Share Posted October 15, 2022 No sealant should ever be needed on an AN fitting ever. There are hundreds of millions of AN fitting assemblies flying around the world with no leaks. It may be that the flare on the tube is incorrect. I have used a steel male fitting to tighten against the aluminum flared tube to slightly reform the flare with success. The only time I have ever seen a leaking AN fitting that was properly made was on a Gulfstream. It had a deep scratch on the male fitting flare surface causing the leak. This issue should be easy to resolve and flared tubes are easy to make. An fittings are 37° flare angles. Quote Link to comment Share on other sites More sharing options...
Anticept Posted October 15, 2022 Report Share Posted October 15, 2022 Gonna go with what Tom and Madhatter said; if an AN fitting is leaking when it's been properly torqued, it's either the flare is bad or the metal mating surface is. Usually if that comes up, someone either torqued the hell out of it and deformed the flare, or the installer did a poor job with the flare tool. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted October 15, 2022 Report Share Posted October 15, 2022 This does look like the screwed in tank fitting and not the flared end. You may not want to use a sealant, but it works very well just like using other sealants on many other fittings and threads with coolant, oil and fuel. Hylomar is meant for use around fuel. I use Hylomar on the fuel bulkhead fuel supply fitting threads too. Just like where yours is coming from. I have NEVER had a repeat fuel leak after applying Hylomar to those threads and fitting base. That means these fittings have been doing well since 2007 (15 years). Seems to me it works. FD uses Hylomar too, maybe not on this application, but it works very well. If you've never used it in these areas or experimented with it in these areas how can you pass judgment since it's been used on at least 75+ aircraft with not a single issue. I used it on a CTLSi fuel return line last spring. Still no issue and it sealed the leak without fail. Quote Link to comment Share on other sites More sharing options...
Anticept Posted October 15, 2022 Report Share Posted October 15, 2022 Sealant on the bulkhead tank adapter threads is perfectly fine by me. Don't get me wrong on that! What we were saying is it doesn't go on the flare or the threads of the B nut (blue nut); AN fittings are designed for metal to metal sealing and they're incredibly good at the job... so good at it that they're rated to truely rediculous pressures. Someone really fucked up the fitting or tubing if they leak. Putting sealant inside of an AN fitting is like JB Welding an engine oil leak; it might work but it is probably covering up a more serious issue, and the next mechanic who works on it might be confused at seeing the goo. Quote Link to comment Share on other sites More sharing options...
Mike Koerner Posted October 15, 2022 Report Share Posted October 15, 2022 In the lab where I used to work we had test stands with flared stainless steel fittings and tubing that was used over and over again. Over time they'ed get damaged. The technicians used seals between the flared surfaces, such as are shown here. They replaced the seals every time they reassembled the fittings. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted October 15, 2022 Report Share Posted October 15, 2022 If the FAA found someone using sealant on certified aircraft fuel AN fittings to stop fuel leaks it would probably result in some sort of certificate action. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted October 15, 2022 Report Share Posted October 15, 2022 As mike pointed out they do make a special soft aluminum seal for flare fittings, they are called a DEL seal. I remember using them on the A/C installation in a Baron. https://www.aircraftspruce.com/catalog/hapages/del37fittings.php Quote Link to comment Share on other sites More sharing options...
Bill3558 Posted October 16, 2022 Author Report Share Posted October 16, 2022 I used some Permatex #2 on the threads and it appears to have fixed the leak. Thanks for all the suggestions. Quote Link to comment Share on other sites More sharing options...
Anticept Posted October 16, 2022 Report Share Posted October 16, 2022 On 10/15/2022 at 10:20 AM, Tom Baker said: As mike pointed out they do make a special soft aluminum seal for flare fittings, they are called a DEL seal. I remember using them on the A/C installation in a Baron. https://www.aircraftspruce.com/catalog/hapages/del37fittings.php That's neat. I'll keep these in mind. Quote Link to comment Share on other sites More sharing options...
FredG Posted October 16, 2022 Report Share Posted October 16, 2022 They are also sold by Pegasus Auto Racing as "SECO 7, AN 37 Degree Flare Seal." I used quite a few when building my RANS S-20. Any fitting that would be difficult to access once built got such a seal. Pegasus has them in aluminum and copper (they recommend copper for steel fittings). Quote Link to comment Share on other sites More sharing options...
Anticept Posted October 24, 2022 Report Share Posted October 24, 2022 Found millspec part numbers for these flare inserts. AS4824 for 37 degree flares and AS4825 for flareless. https://gen-aircraft-hardware.com/images/PDF/flaresaverkit.pdf Quote Link to comment Share on other sites More sharing options...
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