Fuel distribution block - pressure gauge line

Discussion in 'Maintenance Bay' started by 455 Bravo Uniform, Nov 18, 2017.

  1. 455 Bravo Uniform

    455 Bravo Uniform Cleared for Takeoff

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    Taking the top cowl off to start my oil change this afternoon, I noticed blue staining on top of the engine. Traced it to the fuel pressure gauge line as it comes off the distribution block. It looked like it was leaking where the line attached to the 90 degree male AN flare, but the connection was tight. Found a tiny fracture in the line about a quarter inch from the flare. I am guessing from vibration fatigue or multiple cycles of removal & replacement or poor forming or faulty install.

    All of the lines to the injector look like stainless, but the pressure line looks like copper. Are these lines always copper? In my racecars I always used braided stainless hoses with AN fittings, for this very reason.

    I've also heard copper can "work harden" over time due to flex cycles, but I don't really know anything about that.

    Not sure what I'm asking, but just throwing it out on the web for any similar experiences or knowledge about aircraft fuel systems.
     
  2. Dan Thomas

    Dan Thomas En-Route

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    Copper is not good. It work-hardens and cracks quickly. You might have what is known as Everdur, a copper-coated steel line that is much tougher than copper. In any case, the line was probably not adequately supported to stop the flexing that broke it.
     
  3. 455 Bravo Uniform

    455 Bravo Uniform Cleared for Takeoff

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    Thank you. What should the line be made of? Everdur or something else?

    I will have my A&P replace it.

    Surely it could be zip tied to the other ss lines on its way to the firewall?

    I'm now thinking about the line inside the cabin going to the fuel flow gauge. I used to run isolators filled with antifreeze in my cars.
     
  4. Clark1961

    Clark1961 Touchdown! Greaser!

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    Dan will have a better answer but never zip tie a metal fuel line. It will cause a failure eventually.
     
  5. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    All metals work harden, nature of the beast. Hardened metals have their drawbacks and benefits.
     
  6. mondtster

    mondtster Pattern Altitude

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    This is what adel clamps are meant for.
     
  7. 455 Bravo Uniform

    455 Bravo Uniform Cleared for Takeoff

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    Went back to the hangar tonight and my hangar neighbor was there. His has hoses.

    image.jpeg
     
  8. mondtster

    mondtster Pattern Altitude

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    The fuel pressure (flow) lines I've dealt with have had an orifice in them to restrict flow. If the line breaks you'll get a little fuel out of it but not as much as you would from a simple open line. It may also be used to dampen any pulsations that would cause a gauge to twitch.

    As a side note, I've seen some of these fuel flow gauges quit working in cold weather, presumably because there is some water in the pressure line going to them that has frozen. Oftentimes they will start working once the engine compartment and cabin start warming up. I would not accept this as being ok however, because you don't know if the line is broken (and leaking fuel) or if it is just frozen.
     
  9. 455 Bravo Uniform

    455 Bravo Uniform Cleared for Takeoff

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    Makes sense. The hole in the elbow that the line was connected to has a tiny orfice.
     
  10. Dan Thomas

    Dan Thomas En-Route

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    The line should be whatever the parts manual says it should be. If it's copper, some mechanic might have made a change from the proper line because the proper stuff wasn't readily available, or was too expensive, or he had some copper laying around. None of those are good reasons.

    No zip ties. They're not only hard on the line (grit gets embedded in them and chafes at the metal) but the heat above the engine after shutdown will cook them in short order. Adel clamps are the accepted method, and the clamps shouldn't be anchored to something else that might move, like another line.
     
  11. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    Abrasives get under Adel clamps also. The aft airstair area on the 727 was a sure place to find worn tubing at Adel clamps.
     
  12. Dan Thomas

    Dan Thomas En-Route

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    I've seen that, but it was because of Adel clamps that were too large to start with, or they were so old that the rubber had taken a set and no longer gripped the tubing. Stuff like that is supposed to be caught at annual inspections. Often they're ignored and in the end the owner pays for new parts--sometimes very expensive parts like an engine mount--instead of new clamps once in a while. A properly installed and inspected clamp won't cause damage.
     
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  13. JAWS

    JAWS Pre-takeoff checklist

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    What make and model?
     
  14. 455 Bravo Uniform

    455 Bravo Uniform Cleared for Takeoff

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    Continental IO-470
     
  15. JAWS

    JAWS Pre-takeoff checklist

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    Is it a solid line to the baffling and then a hose to the firewall?
     
  16. 455 Bravo Uniform

    455 Bravo Uniform Cleared for Takeoff

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    No, solid on both sides of the baffling.
     
  17. JAWS

    JAWS Pre-takeoff checklist

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    YIKES! That doesn't seem right. Better start researching that.
     
  18. bnt83

    bnt83 Final Approach

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    Sometimes the type design is bad design. Yes there are type design approved rigid lines tp engines on some aircraft. Some of them carry fuel or oil, its a bad design plain & simple.

    Similarly a big jet maker had an AD come out on their airplanes the other day because the type design sealant used on the fireproof APU enclosure is FLAMAMBLE. APU= aux power unit aka small turbine engine.
     
  19. Bell206

    Bell206 Pre-takeoff checklist

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    455:
    www.csobeech.com/files/TCM-470-PartsManual.pdf

    Fuel stuff starts on manual page 2-94 or pdf page 124.

    FYI: the plastic "Ty-Raps" in your pic above not a good idea on the fuel line.
     
  20. 455 Bravo Uniform

    455 Bravo Uniform Cleared for Takeoff

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    Thank you all.
     
  21. JAWS

    JAWS Pre-takeoff checklist

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    I think the fuel flow (fuel pressure) line is an airframe part. You would need the IPC for the aircraft to find the part number. Also might want to check into service bulletins to see if there is a ready made change from hard lines to hoses for the aircraft.