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Jim Feldmann
Joined: 01 Sep 2008
Posts: 54
Location: Burbank, CA
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 Posted: Mon May 11, 2009 7:27 am Post subject: Fuel Line Growing |
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I just replaced all of the flexible fuel lines (wing tanks to header and firewall forward) with new Goodyear SAE 30R7 rubber fuel line. After a day or two I noticed that the lines seemed to have gotten longer, so I did a test.
Immersing a 3" long piece of fuel line in fuel for 48 hours caused it to grow to 3 1/8" long. I put a piece of Gates SAE 30R7 in with it, and it grew by exactly the same amount. Fortunately, the ID increased as well, so I am not immediately concerned that it will restrict the fuel flow, but clearly, the fuel is infiltrating the rubber.
The fuel I'm running right now is 50% 100LL, 50% 91 octane autogas and the appropriate amount of Decalin. There is no measurable ethanol in the mix.
It's been warm here, so I did a control test to see if temperature would cause expansion and contraction. I put a second 3" sample of each brand in the refrigerator for 48 hours. No change in the length of either one.
Has anyone experienced this.
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Jim Feldmann
Kitfox IV Speedster / 912 lost to prop failure
Building a Kitfox 5 Voyager |
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Mon May 11, 2009 7:57 am Post subject: Re: Fuel Line Growing |
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| Jim Feldmann wrote: | I just replaced all of the flexible fuel lines (wing tanks to header and firewall forward) with new Goodyear SAE 30R7 rubber fuel line. After a day or two I noticed that the lines seemed to have gotten longer, so I did a test.
Immersing a 3" long piece of fuel line in fuel for 48 hours caused it to grow to 3 1/8" long. I put a piece of Gates SAE 30R7 in with it, and it grew by exactly the same amount. Fortunately, the ID increased as well, so I am not immediately concerned that it will restrict the fuel flow, but clearly, the fuel is infiltrating the rubber.
The fuel I'm running right now is 50% 100LL, 50% 91 octane autogas and the appropriate amount of Decalin. There is no measurable ethanol in the mix.
It's been warm here, so I did a control test to see if temperature would cause expansion and contraction. I put a second 3" sample of each brand in the refrigerator for 48 hours. No change in the length of either one.
Has anyone experienced this. |
The last time I used the black rubber automotive line was years ago, so don't know if it did this. I'd certainly be very concerned tho - this doesn't sound like something I'd want to happen in an airplane fuel system......
The main problem with the black rubber line, besides the fact that it can't be inspected, is it's pleated - the pleats can separate under vacuum and the inner wall can collapse with disastrous results. Don't ask my why I know this.
The only opaque stuff I'd run would probably be Aeroquip and I'd use that in places where replacing it regularly is very difficult or impossible.
I now use Tygothane fuel line which is designed for applications under vacuum like ours generally are. And it doesn't require special fittings like aeroquip does.
LS
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JOE RONCO
Joined: 04 Aug 2007
Posts: 31
Location: CENTENNIAL COLORADO
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| Posted: Mon May 11, 2009 8:52 am Post subject: Fuel Line Growing |
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JIM: Goodyear says for SAE30R9 "WARNING: Do not immerse in gasoline". Both 30R7 and 30R9 have the same outer cover (Black Hypalon-see attached Spec Sheets) so maybe the same warning applies to both? Just a guess. You could also contact Goodyear by phone or e-mail and ask about it. See:
http://www.goodyearep.com/contactus.aspx
Let us know what they say if you do.
Joe R
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Jim Feldmann
Joined: 01 Sep 2008
Posts: 54
Location: Burbank, CA
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| Posted: Tue May 12, 2009 8:39 am Post subject: Re: Fuel Line Growing |
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Thank you both for your replies.
I had sent Goodyear an email before my first post, but got no reply. (I told them the installation was on an airplane, so I suppose I shouldn't have expected one.)
Using the link that you posted, I called them and spoke to the "tubing specialist". They were very friendly and helpful, by the way. He said that there is some permeation of the fuel into the rubber, and that some expansion is normal. Delamination should not occur. And yes, total immersion in gasoline is not recommended because the outer cover is not "gasoline proof", but is there for strength and abrasion resistance.
My installation does not use the tubing immersed in fuel, so I am not going to worry about it. I will make it a part of my normal pre-flight to check for deterioration of the fuel lines and to check the fuel flow rate at the gascolator.
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Jim Feldmann
Kitfox IV Speedster / 912 lost to prop failure
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jetboy
Joined: 22 Jul 2006
Posts: 233
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| Posted: Sat May 16, 2009 1:09 am Post subject: Re: Fuel Line Growing |
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Problem I've had is the lines going hard after a year. This happened whether the fuel was auto 91, avgas100/130 , Jet-A, Jet-B. The Goodyear lines seem to be less affected, most of my lines are USA Gates because they are available locally at the auto & marine places. They dont leak or have any service problems as such, just not as pliable as when new and I tend to replace them if they need to be undone for any reason.
Ralph
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Jim Feldmann
Joined: 01 Sep 2008
Posts: 54
Location: Burbank, CA
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| Posted: Sat May 16, 2009 7:10 am Post subject: Re: Fuel Line Growing |
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I have Gates and Goodyear available. I noticed that the Gates cuts much easier than the Goodyear, so I use the latter on the theory that it would be better able to resist abrasion.
Yes, I have noticed that it gets hard after a period of time. That is why I replaced it.
To finish the report, I took the short samples out of the gasoline and let them dry out for a couple of days. They both went back to exactly 3" in length. FWIW.
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Jim Feldmann
Kitfox IV Speedster / 912 lost to prop failure
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ami(at)mcfadyean.freeserv
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| Posted: Sat May 16, 2009 11:22 am Post subject: Fuel Line Growing |
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Posted: Mon May 11, 2009 7:57 am Post subject: Re: Fuel Line Growing
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Lucien wrote:
<<I now use Tygothane fuel line which is designed for
applications under vacuum like ours generally are. And it doesn't require
special fittings like aeroquip does.
LS??
I find that Tygothane (i.e. polyurethane) fails after about 5
years. Apart from very slow creep under clips etc., the material develops
numerous longitudinal hairline cracks (usually from the outside and inwards
(not due to UV), then starts to leak.
Duncan McFadyean.
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Sat May 16, 2009 1:28 pm Post subject: Re: Fuel Line Growing |
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| ami(at)mcfadyean.freeserv wrote: |
LS??
I find that Tygothane (i.e. polyurethane) fails after about 5
years. Apart from very slow creep under clips etc., the material develops
numerous longitudinal hairline cracks (usually from the outside and inwards
(not due to UV), then starts to leak.
Duncan McFadyean.
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Well I replace long before that, tho. Generally at least every 2 years. My fuel system is very simple tho and regular replacement isn't too hard to do. Being able to inspect the lines is more important than a lifetime beyond 5 years.
If I did have fuel lines in places I couldn't get to easily, I'd go ahead and bite the bullet for aircraft grade lines and fittings for those parts (i.e. aeroquip)....
LS
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LS
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