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  #1  
Old 03-12-2015, 03:16 PM
crabandy crabandy is offline
 
Join Date: Jan 2010
Location: Ottawa, Ks
Posts: 2,349
Default Cracked Fuel Line Flare

During preflight this morning I caught a faint fuel smell when I opened the canopy, I re-adjusted the seat backs and thought I could still smell a bit of gas. There is a bit of a gap around the fuel selector cover and with a flashlight I thought I could see a bit of moisture. After I removed all the covers and started pumping fuel through the lines I found fuel seeping out the outlet connection of the fuel valve going forward to the fuel filter and fact pump. After removing the fuel line there was no visible crack, after a little bit of prodding I found it.




I literally just finished my first condition inspection, just over an hour flight time since unbuttoned everything up. During the condition inspection there was no sign of any fuel from the previous 96 hours, all connections were tight and I pumped the remaining fuel out of the tanks with the boost pump while everything was opened up looking for leaks.

I remade my original lines prior to final assembly after reading this post several years ago:
http://www.vansairforce.com/communit...ad.php?t=78240

I made the flares with the Rigid RFT37 and this "how to:"
http://www.gen-aircraft-hardware.com...ess_Tubing.pdf

I thought I did a decent job, perhaps not. It is the line I bend slightly to remove my Earls 85 Micron inline fuel filter, is it possible that slight bending of the fuel line without loosening the flare nut on the fuel selector would cause this? I tightened via the Flats From Wrench Resistance charts, did I over tighten it?

Thanks,
Andy
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Last edited by crabandy : 03-12-2015 at 03:23 PM.
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  #2  
Old 03-12-2015, 04:23 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,364
Default Bad Flare.

It looks like it is possible the flare was overly thin in the beginning. I just went to the shop and torqued, over torqued actually, a connection on spare material I have, then removed the nut inspected and repeated. I don't think there is any way that torque alone did this, it was the result of the flaring process. Make a few and measure the flare thickness.

To be sure, make a new a flare and measure the diameter and thickness of the flange before and after, then deliberately over torque and remeasure. Then repeat.

YMMV
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  #3  
Old 03-12-2015, 04:39 PM
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Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 16,167
Default

Quote:
Originally Posted by crabandy View Post



I made the flares with the Rigid RFT37 and this "how to:"
http://www.gen-aircraft-hardware.com...ess_Tubing.pdf

I tightened via the Flats From Wrench Resistance charts, did I over tighten it?

Thanks,
Andy
From the photo, it looks like the material is very thin where it cracked, compared to the outer bell of the flare.

The tutorial you linked if for stainless------------lot harder than alum---------did you possibly overdo the flaring operation following the stainless instructions exactly?
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Last edited by Mike S : 03-12-2015 at 04:42 PM.
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  #4  
Old 03-12-2015, 04:47 PM
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Vlad Vlad is offline
 
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Location: Utah
Posts: 8,482
Default What Bill said

I had exactly the same problem with a brake line early in the build.






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  #5  
Old 03-12-2015, 04:54 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
Posts: 7,903
Default

To my eye there appears to be a change in the flare angle, starting at the crack. Are you sure you used an aviation flare, not an automotive one? They're different angles.
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  #6  
Old 03-12-2015, 05:12 PM
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JonJay JonJay is offline
 
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Location: Battleground
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Default

Quote:
Originally Posted by crabandy View Post
I thought I did a decent job, perhaps not. It is the line I bend slightly to remove my Earls 85 Micron inline fuel filter, is it possible that slight bending of the fuel line without loosening the flare nut on the fuel selector would cause this? I tightened via the Flats From Wrench Resistance charts, did I over tighten it?

Thanks,
Andy
I don't think so Andy. This is a common set up and I have been removing my filter having to slightly bend the line out of the way to get the filter out for a long time.
I think the other folks have some good ideas to check.
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  #7  
Old 03-12-2015, 05:43 PM
crabandy crabandy is offline
 
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Location: Ottawa, Ks
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Looks like it's time to play with the flaring tool some more, very possible I just over-flared. If I recall correctly I set the tubing flush with the top of the flare tool, lubricated and rotated 1/2 turn forward and 1/4 turn back until the clutch broke free. I did have to file down the flare to get the Bnut to slide over the flare on some of my connections.

BillL,
I found the max diameter I'm shooting for (basically the Bnut slides over it), what about the thickness of the material?

Thanks,
Andy
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  #8  
Old 03-12-2015, 05:52 PM
TS Flightlines TS Flightlines is offline
 
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Location: Ridgeland, SC
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My .02 worth. 3003 does get pretty thin after flaring, both at the mouth of the flare, and the contact point where the male seals. This is especially true when you tighten the flaring tool to make the flare. You think that tighter is better, but actually the flaring cone is thinning out the material. Combine that with the sleeve pressed against the back side of the flare AND at the inner point of the flare. So when you tighten the nut, the sleeve compresses an already thinned and soft tube. Add some repeated disassemblies, and maybe some minor misalignment, and oops, we have an issue.
We use 304 stainless, and 5052-O aluminum, for the extra strength.
If you are going to use 3003, try NOT cranking down on the flaring cone when the flare is made. Inspect this closely, paying attention to the inner area of the tube as well as the wall thickness at the mouth. If its .020 or less, dont use it--it will eventually fail.

Again---my .02 worth.
Tom
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  #9  
Old 03-12-2015, 06:12 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by crabandy View Post
I think a key to the problem lays in the diameter change of the tube right below where the flair angle starts.
There should not be a step in the tube diameter at this location.
I suspect this was caused by one of two things.

1. The B nut was tightened excessively which caused the sleave to compress a portion of the flair, leaving the step that is visible at the base of the flair.

2. The flairing tool you used is not forming the flair properly.
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  #10  
Old 03-12-2015, 06:58 PM
BillL BillL is offline
 
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Location: Central IL
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Quote:
Originally Posted by crabandy View Post
Looks like it's time to play with the flaring tool some more, very possible I just over-flared. If I recall correctly I set the tubing flush with the top of the flare tool, lubricated and rotated 1/2 turn forward and 1/4 turn back until the clutch broke free. I did have to file down the flare to get the Bnut to slide over the flare on some of my connections.

BillL,
I found the max diameter I'm shooting for (basically the Bnut slides over it), what about the thickness of the material?

Thanks,
Andy
I think the issue is the clutch release. I used a 45 deg version of this tool from the rental store. I lubricated it do the tip rotated free and the threads were clean but oil coated. I flared some 3/4" hard copper for my air compressor. Both on this tool and the my 37 deg Parker Roloflare, when operating correctly it is a light touch to realize when the flare is complete, only a slight increase in torque, this 3003 aluminum is quite soft and weak.

My flare flange is the same diameter as the sleeve, and thickness is only slightly less than the tubing itself. Do a couple with the "feel" in mind and you will quickly recognize when the flare is complete. Over torque one and look at it too.

Edit: I measured a few flare flange thicknesses - all were virtually the same as the tubing thickness - 0.35"
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Last edited by BillL : 03-12-2015 at 07:05 PM.
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