-6 AN fuel lines and fittings

[Spieg]

I'm thinking about converting all the flex lines in my fuel delivery system. Anyone got pros v cons?

I'm thinking of getting these to connect to the hard lines


And these to connect to the braided hose


And these to connect to the engine fuel rail


I've also considered using a NPT standard fitting rather than -6 AN, but there seems to be a larger selection for the AN standard.

Anyhow, just wanting to know if anyone has another preference for a reason I am not thinking of. Or would I be just as well to go with plain old rubber EFI hose and clamps?

 

[mysunnshine]

With ethanol in the fuel now, it's safer to use PTFE hose(teflon lined) instead of the traditional braided hose or rubber hose. You can get PTFE hose ends with aluminum fittings now too. Every project I do now, I use PTFE hose. The regular rubber or braided hose breaks down from the inside out due to the ethanol and failure will eventually happen. The PTFE hose is ethanol compatible.

 

[AJM81CJ8]

I would suggest using stainless fittings. The ethanol will cause the aluminum fittings to corrode eventually. Also, make sure you use the correct flaring tool. AN is not the same angle as automotive. AN is 37* and automotive is 45* IIRC.

 

[mysunnshine]

How long would/does it take to erode aluminum fittings?

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[zr10054]

I used Teflon coated flex lines and alum fittings on my Stump Jumper project. Those fitting will outlive me. I believe most carbs and throttle bodies are Aluminum.

 

[Spieg]

So I'm looking at Teflon hose and fittings and ran into another question. What's the deal with conductive VS non-conductive Teflon? The conductive is supposed to eliminate the risk of static charge building (something about gas flowing through a non conductive tube builds static charge). Of course the conductive hose costs a lot more than the already expensive ($6 a foot!!) non-conductive PTFE hose. I'm just wondering if the risk of static charge is a legitimate concern, would they even sell the non-conductive stuff?

 

[AJM81CJ8]

@mysunnshine- it would depend on a number of factors, but I work in aviation, and aluminum corrosion can and has happened very quickly. We've seen some pretty severe corrosion on customer's planes show up in 4 years. Areas that I have personally inspected, then 4 years later I inspected again, resulting in major structures repairs. That being said, as far as aluminum fittings are concerned, I know that the OEMs use either plastic or stainless for any fuel lines, as they are concerned about alcohol in the fuel reacting (providing an oxidizer) with the aluminum.

 

[mysunnshine]

Yes most all of the automotive has converted to stainless.


Here's an experiment that I started in February. I have a chunk of aluminum in a glass jar that is filled with E85. I did this because I wanted to know the long term effects on aluminum such as fittings and fuel tanks. I specifically wanted to know if the fuel tanks scale and may possibly clog a fuel filter. So far, no change yet- 😎

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[Spieg]

I would suggest using stainless fittings. The ethanol will cause the aluminum fittings to corrode eventually. Also, make sure you use the correct flaring tool. AN is not the same angle as automotive. AN is 37* and automotive is 45* IIRC.

Yep, AN is 37*. I don't think stainless fittings are an option for PTFE hose (at least not that I've found). Russell, Earl's, etc... only offer aluminum with a variety of anodizing options. Aeroquip only offers steel (the rusty kind).

 

[mysunnshine]

There are stainless fittings available for PTFE hose.

@AJM81CJ8. I'll assume that the corrosion that you are talking about is external airframe that would be exposed to salty air right?

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[AJM81CJ8]

What alloy of aluminum are you using? Is it clad? Different alloys have different propensity for corroding. For example 2024 alloy, where copper is the primary alloying agent, doesn't corrode as easily as say 7075 alloy, where magnesium is the primary alloying agent, tends to exfoliate fairly easily. Looking on both Earl's and Aeroquip's websites has not yielded what alloy they use for their fittings, so it is had saying. Most fittings are anodized in one form or another, so as long as the coating remains intact, usually the fitting can last indefinitely. It's when the protective coating is compromised that issues begin to happen.

 

[AJM81CJ8]

@AJM81CJ8. I'll assume that the corrosion that you are talking about is external airframe that would be exposed to salty air right?

Sometimes, although "salty" air isn't necessary. I specialize in "wide body" Bombardier business jets (Challengers and Global Express). We have found corrosion inside the cabin from water leakage from potable water systems, from condensation from cool fuel in tanks and warm, moist air in the aft equipment compartment, and inside of integral fuel tanks from entrained water in Jet fuel. It is a constant battle to keep the "Aluminium Worm" at bay. Hence the reason why I'm not to keen on Aqualu tubs. Beautiful workmanship, I'm just not a fan of aluminum for car bodies, espcially up here in salty Michigan.

 

[mysunnshine]

So your concern is more for the external corrosion rather than the internal corrosion from the E85?

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[AJM81CJ8]

Both, kind of. The concern I have on the internal side would be E-85 and any air that might get into the lines. I guess without a real world test it would be hard saying what would happen in the long run. As far as external corrosion, I'm probably a little too cautious, as I don't drive my Jeep in the winter, so salt exposure is kept to a minimum.

 

[cbford]

This answers a lot of the questions raised.
http://www.nmma.org/lib/docs/nmma/gr/environmental/E20_Position_Paper.doc

Basically, it is not the ethanol; it is the water that the ethanol holds in the fuel that causes oxidation changes, builds static electricity and is general trouble for filters.
If you want to use hose; it doesn't necessarily have to be PTFE lined. SAE 30r9 rated hose is available from several places. It is flouroelastomer lined to work same way and is cheaper. SAE 30r10 rating is for submerged hose applications like in tank.

I also notice a lot of nylon tubes and fittings on OEM stuff now. When I built my fuel system, I used nylon hose that I wrapped in insulation with nylon snap lock fittings on the ends for connections at tank, filter, fuel rail and regulator.

 

[CJ7Pilot]

I'm not a chemist, but I think most corrosion requires exposure to air (oxygen).

Maybe (time permitting) you should parallel this test with a piece of aluminum dipped in E85 every day, then allowed to dry.

After all, sometimes fuel tanks are full... but most of the time they are closer to empty....

 

[Belizeit]

AJM81CJ8 & CJ7Pilot are correct. I grew up on an island right next to a large barrier reef with salt thick in the air and clinging to everything. I was around airplanes and boats a lot. I never saw a piece of metal that didn't rust or corrode. Some starting over night after coming from the States.


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[Spieg]

I've continued looking into PTFE lines and my research indicates it is a VERY bad idea to use regular "white" PTFE for fuel (unless you like fire and explosions). Guess I'll suck it up and shell out for the "Black" carbon impregnated PTFE.

Also, I did find some PTFE hose ends made of stainless steel although they are a brand name I've never heard of (probably made in China) and I don't know if I trust that. If anyone can steer me toward a manufacturer they have used and recommend, I'd be grateful.

 

[AJM81CJ8]

Check with www.aircraftspruce.com for AN fittings. Aviation certified parts are going to be of the best quality and consistency as far as manufacturing.

 

[zr10054]

It's a Jeep for God's sake. LOL