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  #1  
Old 08-02-2021, 07:01 AM
LettersFromFlyoverCountry's Avatar
LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Location: St. Paul, MN.
Posts: 4,826
Default Fuel line bending

It never fails that every year on the day the Lindy Award winners are announced, I go back to the hangar to redo something on whatever plane I'm building that I might have been generally dissatisfied with.

This year it was the fuel tank. I had used EZ Turn on fitting threads (which we used to do and consider it acceptable) and I wanted to fix that. And I did, replacing it with Permatex 2.

But in reinstalling it, I badly nicked the fuel line when trying to get a crowsfoot on the fuel line fitting at the tank. So I pulled it off, ordered new tubing and tried to remember how the heck I made that line in the first place.

Here's why.



The instructions say:
1. Flare the tank end of the tube.
2. Make the bend
3. Install the nut and sleeve from the pump end of the tube.

The problem is you can't (at least *I*) can't slip a sleeve over a 38 degree bend. And yet somehow I made this line two years ago. I just can't remember what I did. (Yes, I know the sleeve is on backwards in the above photo)

Putting the collar on first and then making the bend seems problematic as the end of the bend line is 21/32" from the end of the tube.

Maybe I put the collar on, made the bend, and THEN flared the tube. I don't know.

What's the secret here?
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  #2  
Old 08-02-2021, 08:31 AM
rapid_ascent rapid_ascent is offline
 
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Default

I think you may need to do the flare first then the bend. If you try to do it the other way around you will need the length of the sleeve plus the thickness of your flaring tool to be less than you 21/32" dimension. I don't think that will work. Some folks have modified a bender tool to allow the flare to be positioned back into the bender. Tom had this as a recommendation some years back. This can help getting short bend distances.
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  #3  
Old 08-02-2021, 09:11 AM
PilotjohnS PilotjohnS is offline
 
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Default Just me

I would take the straight tube, put the B nut and collar on, flare it.
Then put it on a union, and hand bend the curve, gently
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  #4  
Old 08-02-2021, 02:58 PM
WenEng WenEng is offline
 
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Location: Jacksonville, FL
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Default You can shorten the sleeve

I have seen where the sleeve has been cut back with dremel wheel cutoff disc so a minimum is showing outside the BNut. That shortened length allows slipping over curves that would not otherwise be possible. If you have an extra sleeve, give it a try. Otherwise I would do what John recommended and hand bend it last.
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  #5  
Old 08-03-2021, 05:58 AM
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BobbyLucas BobbyLucas is offline
 
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Default

Quote:
Originally Posted by WenEng View Post
I have seen where the sleeve has been cut back with dremel wheel cutoff disc so a minimum is showing outside the BNut. That shortened length allows slipping over curves that would not otherwise be possible. If you have an extra sleeve, give it a try. Otherwise I would do what John recommended and hand bend it last.
This is what I did, except I still put the sleeve on before bending - I just trimmed it so that the tube could slide further into the bender. (I can't recall if I thought to try sliding the shortened sleeve around the bend, but if that works it would definitely be easier.) I then inserted a properly sized drill into the end of the tubing to act as an extension. These two steps allowed me to get the bend as close to the end of the tube as possible, ultimately matching the drawing. I obsessed way to much over this one bend.
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  #6  
Old 08-03-2021, 06:15 AM
MDeCraene13 MDeCraene13 is offline
 
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Default

This is not an answer to your question, but what do you mean when you say the sleeve is on backwards in the picture?

It looks like the normal orientation to me.

I also don't follow your comment about using permatex on flared fitting threads. I am not familiar with the -12 fuel tank, so it may be that you are referring to a different fitting than the rest of your post.

Thanks for helping me understand.
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  #7  
Old 08-03-2021, 07:05 AM
N8DAV8R N8DAV8R is offline
 
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Quote:
Originally Posted by MDeCraene13 View Post
I also don't follow your comment about using permatex on flared fitting threads. I am not familiar with the -12 fuel tank, so it may be that you are referring to a different fitting than the rest of your post.
I'm starting this section in the next few days and this threw me back into a loop of doubt too.
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  #8  
Old 08-03-2021, 07:30 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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The fitting to which this line attaches.

The NPT threads of the fitting into the tank. Not the threads to which the B nut attaches.

Section 5.27.
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Last edited by LettersFromFlyoverCountry : 08-03-2021 at 08:29 AM.
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  #9  
Old 08-03-2021, 08:34 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Quote:
Originally Posted by MDeCraene13 View Post
This is not an answer to your question, but what do you mean when you say the sleeve is on backwards in the picture?
Sorry for the confusion. I thought I was posting another picture. This is the original line.
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Blog: Letters From Flyover Country
RV-12iS Powerplant kit
N612EF Builder log (EAA Builder log)
Last article: "Gonna Finish This Sucker" (Kitplanes)
Waiting for the avionics kit (backordered: chip shortage)
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  #10  
Old 08-12-2021, 11:22 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Default

OK. I give up. I'll pay someone to make this line for me. Anyone?
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Blog: Letters From Flyover Country
RV-12iS Powerplant kit
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Last article: "Gonna Finish This Sucker" (Kitplanes)
Waiting for the avionics kit (backordered: chip shortage)
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