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Teflon fuel line

 
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mtown52(at)gmail.com
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PostPosted: Mon Jun 29, 2020 12:34 am    Post subject: Teflon fuel line Reply with quote

Hi -This is my first question for the forum.
I may use a Teflon fuel pipe with anodized AN fittings in an RV9 between the fuel tank and the Andair fuel selector. The anodized fittings don’t seem to  conduct electricity (even though the teflon fuel line has a metal-braid covered inside a plastic covering). I wondered whether this will be a problem/danger due to possible electrostatic charge from the flowing fuel.
Thanks for any suggestions
Michael Townley
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PostPosted: Mon Jun 29, 2020 5:44 am    Post subject: Teflon fuel line Reply with quote

On Mon, Jun 29, 2020 at 3:38 AM Michael Townley <mtown52(at)gmail.com (mtown52(at)gmail.com)> wrote:

Quote:

Hi -This is my first question for the forum.
I may use a Teflon fuel pipe with anodized AN fittings in an RV9 between the fuel tank and the Andair fuel selector. The anodized fittings don’t seem to  conduct electricity (even though the teflon fuel line has a metal-braid covered inside a plastic covering). I wondered whether this will be a problem/danger due to possible electrostatic charge from the flowing fuel.
Thanks for any suggestions
Michael Townley
--
Mike Townley 0419393470




Interesting question. When Teflon lined hose 1st came on the market, there were significant issues with static buildup due to flow in the non-conductive hose. Because of that, I suspect that you can't even buy Teflon lined hose these days without carbon impregnated Teflon used as the liner. So, while I can't answer your question with authority, I don't worry about it in my installation, since the carbon impregnated Teflon provides a static bleed connection along all components in the fuel system, keeping all the fuel at the same electrical potential.
Thinking about it, if the anodized fittings were a problem, then you'd have the same issue even with aluminum 'hard line', because every joint would be an electrical break in the path. (The male taper of the fitting would insulate from the aluminum female on the tubing.) The old 'rubber' hoses likely had carbon in the liner too, and we never heard about static issues due to anodized aluminum fittings. Shucks, even the anodized fittings may bleed off the static charge, even though they seem to check as open on an ohm meter. 'Static straps' are usually quite high in resistance, so they don't provide a low voltage current path to ground (think about the danger if you're wearing a wrist strap & touch the wrong thing in a circuit....
https://en.wikipedia.org/wiki/Antistatic_device#:~:text=Antistatic%20mat,-An%20antistatic%20floor&text=Typical%20resistance%20is%20on%20the,line%20in%20an%20electrical%20outlet.

I'd suggest checking with your vendor, to be sure that the hose you're planning to use has a carbon impregnated Teflon liner.
FWIW,
Charlie

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PostPosted: Mon Jun 29, 2020 5:58 am    Post subject: Re: Teflon fuel line Reply with quote

No danger from static for a couple of reasons.
Fuel can only ignite if it is mixed with oxygen (air). Since the fuel line does not contain air, it can not ignite. And even if there is air in the fuel line, the ratio of fuel to air needs to be within a certain range to ignite. The mixture will be too rich.
Even if the fuel air ratio is ideal for combustion, there is still no need to worry. A metal airplane like your RV-9 will keep all parts of the fuel system at the same voltage. No sparks will jump. Some fuel systems use non-conductive rubber hose. In that case, the danger is not from static, but from mechanical damage or kinking.
Anodized metal fittings might not be good conductors of electricity, but will conduct enough to prevent high voltages from building up.


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PostPosted: Mon Jun 29, 2020 5:44 pm    Post subject: Re: Teflon fuel line Reply with quote

mtown52(at)gmail.com wrote:
... I may use a Teflon fuel pipe with anodized AN fittings... between the fuel tank and the... fuel selector... I wondered whether this will be a problem/danger due to possible electrostatic charge from the flowing fuel.

Michael Townley


Teflon should have an additive to make it conductive else the flow of a non-conductive medium, like gasoline, will generate an electrostatic charge that will punch holes in the Teflon over time. Rubber hoses are naturally conductive enough and brake lines don't have flow. BTW I have the impression -3 hoses are not available conductive because they are used for brake lines and there is no flow.

Tom Swearengen is an expert you could ask. https://www.tsflightlines.com/about-us.html

Swagelok (I don't mean to advocate Swagelok, just Google got me there.) has some wording that confuses me but they do say "... If the core does not contain carbon black, the media in the hose is electrically insulated from the wire braid, making it possible for a charge to build along the core tube..." https://nwus.swagelok.com/en/products/Hoses_and_Flexible_Tubing/Static-Discharge


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PostPosted: Wed Jul 01, 2020 10:08 am    Post subject: Teflon fuel line Reply with quote

When I tested aluminum parts coming from the paint line at Boeing Auburn all it took was an impedance tester.  Alodining conducts electricity, anodizing does not.

Rick
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On Mon, Jun 29, 2020 at 9:08 AM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

No danger from static for a couple of reasons.
Fuel can only ignite if it is mixed with oxygen (air).  Since the fuel line does not contain air, it can not ignite.  And even if there is air in the fuel line, the ratio of fuel to air needs to be within a certain range to ignite.  The mixture will be too rich.
  Even if the fuel air ratio is ideal for combustion, there is still no need to worry.  A metal airplane like your RV-9 will keep all parts of the fuel system at the same voltage.  No sparks will jump.  Some fuel systems use non-conductive rubber hose.  In that case, the danger is not from static, but from mechanical damage or kinking.
  Anodized metal fittings might not be good conductors of electricity, but will conduct enough to prevent high voltages from building up.

--------
Joe Gores




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PostPosted: Wed Jul 01, 2020 11:13 am    Post subject: Teflon fuel line Reply with quote

What kind of impedance tester? An ohm meter, or a 'megger'?

Even a resistance in the 10s of millions of ohms will bleed off a static buildup. A regular ohm meter might well show an open circuit at those levels.

I still think the terminations issue is moot with currently available Teflon lined hose, since the hose is impregnated with carbon.

Charlie

On 7/1/2020 1:03 PM, Richard Girard wrote:

Quote:
When I tested aluminum parts coming from the paint line at Boeing Auburn all it took was an impedance tester.  Alodining conducts electricity, anodizing does not.

Rick


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On Mon, Jun 29, 2020 at 9:08 AM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

No danger from static for a couple of reasons.
Fuel can only ignite if it is mixed with oxygen (air).  Since the fuel line does not contain air, it can not ignite.  And even if there is air in the fuel line, the ratio of fuel to air needs to be within a certain range to ignite.  The mixture will be too rich.
  Even if the fuel air ratio is ideal for combustion, there is still no need to worry.  A metal airplane like your RV-9 will keep all parts of the fuel system at the same voltage.  No sparks will jump.  Some fuel systems use non-conductive rubber hose.  In that case, the danger is not from static, but from mechanical damage or kinking.
  Anodized metal fittings might not be good conductors of electricity, but will conduct enough to prevent high voltages from building up.

--------
Joe Gores



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PostPosted: Wed Jul 01, 2020 2:02 pm    Post subject: Teflon fuel line Reply with quote

I haven’t seen the original question, but I know that static build up in white Teflon hydraulic lines was causing an arc through to the stainless braid in many helicopter installations. This caused a pin hole that allowed atomised oil to spray into the hot section of the engine, obviously a concern. As Charlie said, the trick was to impregnate the Teflon with carbon to conduct the charge to ground through the fittings. All my -6 fuel and -8 oil lines are black for this reason.

Kind regards, Stu

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Quote:
On 2 Jul 2020, at 05:28, Charlie England <ceengland7(at)gmail.com> wrote:

 What kind of impedance tester? An ohm meter, or a 'megger'?

Even a resistance in the 10s of millions of ohms will bleed off a static buildup. A regular ohm meter might well show an open circuit at those levels.

I still think the terminations issue is moot with currently available Teflon lined hose, since the hose is impregnated with carbon.

Charlie

On 7/1/2020 1:03 PM, Richard Girard wrote:

Quote:
When I tested aluminum parts coming from the paint line at Boeing Auburn all it took was an impedance tester. Alodining conducts electricity, anodizingdoes not.

Rick


Virus-free. www.avg.com

On Mon, Jun 29, 2020 at 9:08 AM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

No danger from static for a couple of reasons.
Fuel can only ignite if it is mixed with oxygen (air). Since the fuel line does not contain air, it can not ignite. And even if there is air in the fuel line, the ratio of fuel to air needs to be within a certain range to ignite. The mixture will be too rich.
Even if the fuel air ratio is ideal for combustion, there is still no need to worry. A metal airplane like your RV-9 will keep all parts of the fuel system at the same voltage. No sparks will jump. Some fuel systems use non-conductive rubber hose. In that case, the danger is not from static, but from mechanical damage or kinking.
Anodized metal fittings might not be good conductors of electricity, but will conduct enough to prevent high voltages from building up.

--------
Joe Gores





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