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Here is a dumb question I expect to go unanswered.  What do I need to know about (both ends of) flare to hose fittings and which are best?  I ask for several reasons, mostly for the oil system, but I think this applies to fuel as well.  I am having a tough time stopping an oil leak at my new Earl’s oil cooler with AN-10 O-ring to AN-8 flare adapters (I don’t think it is leaking at the O-ring, but I notice that the next bigger O-ring would still be snug and fit).  Dell aluminum flare fitting seals from Aircraft Spruce are not helping, if the leak is at the flare.  It is not a big leak, but over time it is making a mess and might introduce air if I let the plane sit too long, requiring purge.

 

Discussion.  AN Aircraft Flare fittings have a 37 degree flare angle (and I have a flare tool that makes this), whereas industrial fittings have a 45 degree angle (and I have a flare tool for this as well), and I see pictures of a mix on some installations (brass industrial mated with painted AN).  Is this ok?   Also, for the hose connections, I see pictures where some people use clamps (Oetiker, worm gear, or fuel injection), some do not.  It appears some are pushed on (push lok?), and some are screwed using a left hand threaded nut and right hand thread barrel with the hose sandwiched between.  Do the push lok and threaded style work well without any clamps (or indeed not supposed to use clamps), and how must they be sized to fit 12.5mm Parker hose (inside and outside diameter for the sandwiched style)? Can I apply lubricant to help get the hose to fitting installed?  Heat (boiling water or heat gun?)?  Do some barbed hose fitting require clamps (like the idustrial ones with rounded barbs), and some specifically not use them?

 

And then, if we use clamps, the fire sleeve does not fit.  Or the band-it clamp would crush the Oetiker clamp if we are not careful.  What then?  Put the band-it further away from the clamp, up on the hose, while stopping short of crushing the hose, leaving a loose band-it clamp?

 

Why do many automotive AN fittings have a hole in the side of the flare nut (showing a shiny piece of metal – and this is most of them)?  Are they as good as the heavier Rotax originals without the hole in the flare nut, and what is the purpose of the hole in the side of the nut? I admit, torqued one down so hard trying to stop my oil leak, it popped apart and I see a retainer ring.  Fortunately the flare nut popped apart on the ground.

 

Sorry for making so much an issue of what apparently is only a problem for me.  I could not find any such discussion.

  • Re: Oil leaks, fittings and hoses

    by » one month ago


    This is not the answer you are looking for but a tip I seen on youtube on how to remove push on hose without damaging the fitting (i.e don't use hacksaw or knife) . Use a soldering gun with a blade like cutting tip. simply cut along the hose longitudinally over the barb part of the fitting, make several light passes not cutting all the way through and the hose will eventually just split and you can pull it off, keeping the fitting like new. comes in handy if you want to reroute hoses after attaching them.


    Thank you said by: Dennis Urban

  • Re: Oil leaks, fittings and hoses

    by » one month ago


    Good tip.  I ruined a fittting trying to get it off.  I already have a hot knife that I never thought of using.  Wish I knew more about these 'new' fittings that are different than the ones I used many decades ago when everybody used hose clamps and hoses slipped on and off easily in the automotive aftermarket world.


  • Re: Oil leaks, fittings and hoses

    by » one month ago


    The first thing you need to determine is where the leak is originating from. ???
    " I Don't Think... " is NOT a valid answer.
    Is it at the Flare Connection, The O-Ring Connection, or the Hose Connection?
    Otherwise, you are just wasting your effort. 
    All of these connections types are time-proven to work when assembled properly.
    They do not need any Redneck Rigging or Aftermarket fixes.

    Clean and Dry the area thoroughly then watch closely to see where the leak originates.
    Then determine why THAT Connection is leaking.
    If it is contamination, Clean It!
    If it is a damaged fitting, Replace It!
    - - -
    Tighten the connections only as much as needed to obtain a seal.
    Overtightening is the largest cause of leaks.
    If you split a Flared Nut, it was Way, Way, Way, too tight!!!
    Properly Designed O-Ring Seals do not need to be tightened at all. Just seated.
    The Oetiker clamp is highly preferred over the Worm Clamp.
    It provides an even sealing pressure around the entire circumference of the connection.
    But don't over-compress it!


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: RotaxOwner Admin, Dennis Urban

  • Re: Oil leaks, fittings and hoses

    by » 6 weeks ago


    One can easily find recommended torque values online, some as ft-lbs, some as "flats" of rotation. Subjectively, firm but not not much of a strain to do with a hand wrench. The fitting that's been over-torqued is now suspect, IMO. Denting or squishing the contact surfaces from that will prevent a good seal. A little under-tight is better than over. Then, if it leaks a little, one can sneak up on a good value, 1/4 flat at a time.


  • Re: Oil leaks, fittings and hoses

    by » 6 weeks ago


    What Bill said plus,

    For fuel hose I use gates vapor recovery or carburetor hose. The fuel injection hose is more reinforced and rated to 100 psi, but doesn't give much when trying to push it over some fittings and scrapes the inner liner and causes tiny debris to float towards the carbs. You do need fuel injection hose for the 912iS engine. The vapor hose is rated to 50 psi and since we only have between 3.5 psi  to 6 psi for the carb engine's that's more than enough and this hose has some give and doesn't cause debris issues when being pushed over some fittings.

    I prefer Oetiker clamps on fuel hose and is an industry standard, but fuel injection clamps work well too. These clamps are well rated for anything we need them for. Some LSA aircraft Mfg's and many other people use fuel injection clamps on our oil hose too. It gives a good 360 degree seal and won't strip or damage the hose. NEVER over tighten any clamp. It can and will cause underlying damage to the hose especially over barbed fittings. 

    I never use the serrated worm drive clamps on any hose. These can over cam and loosen and the serrated openings can cut into the hose. This is old school and some of the certified world just hasn't come into the 21st century yet. :) . I prefer and so do some aircraft Mfg's Wurth Zebra raised rip style worm drive clamps. These give better 360 degree seal, don't cut into the hose and won't over cam and strip out unless you way over tighten them and if you've stripped one of these out you have gone way past any normal torque for a clamp.

     

    https://www.rotax-owner.com/en/rotax-blog/item/21-rotax-5-year-rubber-replacement-the-installation-considerations

     


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


    Thank you said by: Dennis Urban

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