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Thread: Compression Fittings - Remove, Examine, and Reinstall or Must Be Replaced?

  1. #1
    Senior Member Cherrybark's Avatar
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    Default Compression Fittings - Remove, Examine, and Reinstall or Must Be Replaced?

    I just know this thread is inviting controversy so be nice! I have two small leaks at compression fittings.


    • One is where the solid fuel line connects to the fuel shutoff valve at the center console. I've tried gently tightening fitting but, returning to the hanger after a few days, a drop of fuel was hanging off the lowest bend in the tubing and there is a persistent wet spot on the fabric below the fitting. Is it critical that the tubing be exactly in line with the fitting or do the spherical mating surfaces naturally allow a bit of misalignment? Do I just try another 1/8 of a turn or take off the tubing and look for some problem with the flare? Proper flaring angle tool was used. And, of course, there are no leaks forward of the firewall.
    • The second leak was revealed by a film of brake fluid and a single tear of fluid along the horizontal portion of the spring landing gear. This is either where a 90 degree fitting screws into the gear, or the compression fitting on the brake line. My kit came with nylon brake line, compression nuts with captured olives, but no line inserts. There is an old thread discussing these fittings and lack of inserts but I'm trusting that Kitfox sent what they are using in their factory builds, and the supplied components aren't the problem. I can try snugging the compression fittings but that won't help if the leak is where the 90 degree fitting screws into the gear.


    Can I disconnect these compression fittings then reinstall? Or is that a cardinal sin with compression fittings and they must always be replaced?
    Carl Strange
    Flying
    SS7, 912iS, Oratex, G3X

  2. #2
    Senior Member PapuaPilot's Avatar
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    Default Re: Compression Fittings - Remove, Examine, and Reinstall or Must Be Replaced?

    What type of fitting is it at your fuel selector? If it is an aircraft flared fitting then you need those perfectly lined up before tightening the B-nut. Another issue with this type fitting is an improperly flared end with a crack/split or nick in it. Also, are you 100% sure the leak is not coming from the other end of the fuel line?

    For the brake line I would try to tighten the compression nut a little bit. If the leak is at the 90 degree fitting due to looseness, then it should be easy to give it a little turn to test that. Unfortunately if you need another full turn that is going to be challenging, because a full turn on a pipe thread often feels way too tight. You also will have to open the line and bleed the brakes again.

    When looking for leaks I like to clean things up and find the source before the drip has a chance to cover the fitting or run down the line. This often means checking is every minute or so till you see the first evidence.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  3. #3
    Senior Member efwd's Avatar
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    Default Re: Compression Fittings - Remove, Examine, and Reinstall or Must Be Replaced?

    I have disconnected the brake lines at the compression fitting without a problem Carl. I just found a leak at the lowest fitting at the brake caliper where I found two or three drops of brake fluid on the ground next to the tire. I cleaned up the fitting, put a wrench on it and tightened it up only a tiny amount. All is well so far. I had the leaks as you do at the Grove gear. I removed, replaced and reinstalled new fittings with Fuel Lube as the sealer. I know, that isn't what the product is for necessarily but I have a seal at my fittings where I didn't with the blue stuff that was recommended.
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

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