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Hi, I'm thinking of replacing the rubber fuel hoses in my aircraft with teflon coated hoses in places where it's practical to do so.  Teflon hoses, of course, don't fit over barbs, and would need to attach to components with AN thread fittings.

I'm interested in doing this mainly for longevity (some of the areas through which the fuel lines run can be tricky to work on when it's time to replace hoses), and partly because I prefer the security of a threaded attachment over a barb.

Has anyone experience of connecting fuel hoses with AN thread fittings to Rotax engines?  I have a 914 ULS, which has M10 barb banjo bolts on the fuel pressure regulator for the feed and return lines.  I've be really interested in any thoughts on replacing these with AN-6 threaded fittings, and for ideas on where I might source M10 to AN6 threaded banjo bolts.

Thanks!

 

  • Re: AN Fuel Hose Fittings

    by » 3 months ago


    I replaced the fuel hoses to carburetors with Teflon hoses. I purchased them from aircraftspecialty.com. Steve was incredibly helpful. 
    I have no affiliation with this shop. 
    Rich Chesser


  • Re: AN Fuel Hose Fittings

    by » 3 months ago


    I apologise in advance for going of on a tangent BUT:

    Metal hoses (liquid reticulation) are not without their problems -

    (Note: the term "rubber" is a generic descriptor covering all flexible hoses whose primary construction is non metal)

    Threaded connects can & do leak - so can push on "rubber" hoses however both systems are probably equally secure when correctly  installed.

    Metal fatigues - rubber will perish/stiffen over time. The five year replacement for rubber is well within quality rubber hose service life. Metal lines are usually replaced on (visual) condition assessment. Years of vibration/movement can result in a sudden unforeseen failure.

    Metal lines do not accommodation engine movement well (above point) rubber does.

    Metal lines demand very careful periodic support to minimise fatigue related to resonance/movement - rubber is far more forgiving.

    Metal is a good conductor of heat  - not the best characteristic for fuel reticulation. Rubber on the other hand is a natural insulator. I would expect both to have additional heat insulation/shielding where required.

    Metal fuel lines often require joins, where rubber can be a single continues connecter.

    Metal fuel lines requiring special tools for making connection ends and close radius bends - rubber just pushes on and conforms to the contours you want (good idea to have a good quality hose cutter to minimise "shredding" & make good square cuts".

    Metal will cost many times the cost of rubber to install. True the cost will be less every 5 year rubber replacement increments but how many five years periods will it take for rubber to pass the initial cost of metal?

    I would expect metal lines to greater fire resistance however I would speculate that an inflight fire is likely to have a very high mortality rate, no matter what reticulation system is used.

    In most cases of metal line installation, rubber will be used where engine movement needs to be accommodated. This then means additional connector (potential failure) points and adherence to the 5 year rubber replacement.

    There may be other pros/cons I have missed.

    Think again my friend, metal is not all its "cracked" (😁) up to be.

     


    Thank you said by: Joe

  • Re: AN Fuel Hose Fittings

    by » 3 months ago


    Thanks very much Richard and Sean.  

    Totally agree with the points on solid metal tubing.  The tubing I was thinking of using is flexible - similar to rubber.  Some examples:

    https://www.eaton.com/content/dam/eaton/products/fc/flexible-hose-assemblies/eaton-1500-psi-ptfe-hose-assemblies-brochure-tf100-25e-en-us.pdf 

    https://www.goodridge.co.uk/products/goodridge-811-g-line-xf-hose 

     


  • Re: AN Fuel Hose Fittings

    by » 5 weeks ago


    Thanks very much for your replies Richard and Sean (and sorry for my slow response - the website wouldn't let me post for some reason).

    That's all good advice on the solid lines, but in my case, I'm planning on using flexible Teflon hoses with AN fittings.

     


  • Re: AN Fuel Hose Fittings

    by » 3 weeks ago


    Rotax certificated engines come with AN fittings in most locations. Some are easy to source from the Rotax parts diagram, like those going into the newest series mechanical fuel pumps (840770 for example) and the Rotax feed hose (874337 running from the pump to the banjo fitting on the block mounted to the balancing tube between the carbs. Others, not so much. Their absurdly expensive return line, OTOH, is not long enough for my application. The banjo/AN fitting allowing a long return line was apparently a custom piece made by the now-defunct manufacturer. Automotive fittings intended for racing will adapt, but the ones I've found are thicker than the ones Rotax uses. The bolt with the return metering orfice is unique and may be too short to hold the line safely. I do not yet have a solution to offer.


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