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Old 03-14-2009, 01:24 PM
mikeangiulo mikeangiulo is offline
Join Date: Aug 2007
Location: Bellevue, WA
Posts: 51
Default How do you bend 3/8" fuel lines?

I'm having trouble with the fuel line that connects my airflow pump to the firewall. The problem is that the run is short and has a zig-zag (technical term )

If I try and bend it to shape before flaring the straight sections are too short to fit in the flaring tool. So instead i've been cutting the right length, flaring both ends with fittings and then trying to bend it into a Z. Every time I do this, and I've done it four times, the bends collapse a little bit and look squashed. I have a tubing bender but I can't fit the tube into it because the ends are in place.

What am I missing here? I assume the tubing can't be at all collapsed which I think is right and if I try and uncollapse it with seamers it just makes it square. I made all the rest of the hard lines so far with no problem but this little one is driving me nuts.
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Old 03-14-2009, 03:10 PM
Transporter Transporter is offline
Join Date: Jun 2007
Location: Lee's Summit, MO
Posts: 743
Default Fuel Pump Tubing

I made several attempts...but the one that fits the best is two, 180 degree bends at right angles to each other:

Make a sample from coathanger wire or scrap tubing.

Come straight toward the firewall from the pump; make a 180 degree bend in the tubing and come back toward the pump. The 180 degree bend should offset the tubing enough to line up (in a vertical line) with the firewall fitting.

Make a second 180 bend at right angle to the first bend, going back toward the firewall. This bend will line the tubing up with the firewall fitting.

The straight runs should be long enough for you use your flaring tool normally.

It may take another try or two to get the lengths figured out on the straight runs.

I flared the firewall end first, attached the line to the firewall and then marked, cut and flared the pump end.

Good luck,
Mike Dooley
RV hitchhiker
VAF#1067, EAA Chapter 91
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Old 03-14-2009, 03:40 PM
Randy Hooper Randy Hooper is online now
Join Date: Oct 2007
Location: Nashville, TN
Posts: 228

Some times a hard line just will not work. If you run out of Patience and ideas, you might consider fabricating a flex line for the application.

Randy Hooper
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Old 03-14-2009, 04:42 PM
mikeangiulo mikeangiulo is offline
Join Date: Aug 2007
Location: Bellevue, WA
Posts: 51

has anyone thought of doing a full loop (with the fuel line, that is)? I think if I were to use a flexible line I'd have to do something like that or introduce angles or something because the distance that the line would have to zig and back would be pretty tight. It would seem to be a less stressed if it had a full loop but I don't underestimate the secondary effects of introducing design changes (like a new high point to trap air, etc). the two 180 degree method seems pretty reasonable so I'll go give that a shot first but other experiences would be greatly appreciated!
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Old 03-14-2009, 10:51 PM
mikeangiulo mikeangiulo is offline
Join Date: Aug 2007
Location: Bellevue, WA
Posts: 51

Like this?
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Old 03-14-2009, 11:54 PM
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Shockwave Shockwave is offline
Join Date: Mar 2007
Location: Ankeny, Iowa
Posts: 194

I've heard that filling the tube with sand will prevent it from kinking. I haven't tried it myself so I have no direct knowledge of this.

Also a friend of mine has some exterior bending springs that do the same thing. I'm not exactly sure what they're called, but they worked fine for us.
Chanler Childs
Empennage complete
Building wings

Last edited by Shockwave : 03-15-2009 at 12:22 AM. Reason: added content
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Old 03-15-2009, 12:03 AM
robpar robpar is offline
Join Date: Jul 2008
Location: Vancouver British Columbia
Posts: 85

You could use a swivel x JIC Elbow at the pump and another Elbow inline with the bulkhead fitting and then use straight lines between the elbows. The only down side to that is more fittings to make sure they do not leak but the straight lines between would certainly reduce stress on the fittings from those tight bends.

Bob Parry
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Old 03-15-2009, 11:43 PM
rv8_builder rv8_builder is offline
Join Date: Feb 2007
Location: Pretoria South Africa
Posts: 82
Default Two 180 degree bends

We also made several attempts and ended up making two 180 degree bends like Mike.

Hope this helps.
Andre & Nico Burger
South Africa
RV-8 Flying

Our Build Log

Last edited by rv8_builder : 03-17-2009 at 12:06 AM.
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Old 03-16-2009, 07:55 AM
David Clifford David Clifford is offline
Join Date: Jun 2006
Location: Howell, MI
Posts: 220

Although I have never done it before myself, I have been told that filling the tubing with water and freezing it prior to bending works very well in keeping the tubing I.D. nice and round. Make sure you are ready to bend before the ice starts to melt.
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Old 03-16-2009, 02:33 PM
robpar robpar is offline
Join Date: Jul 2008
Location: Vancouver British Columbia
Posts: 85

I have a drawing of the Swivel Elbow idea I had. I saved the SolidWorks drawing as a pdf and a Tiff image, but I seem to be too dumb to figure out how to insert it into my reply.

When I click the insert image icon it asks for an URL but this is a file on my computer and there does not seem to be a way to browse to that file. Of course lots of people do manage, but I guess I need a little help.

If someone can enlighten my I will upload the drawing. It uses a Parker 6-C6X-S, S for Steel but I think Parker makes them in Aluminum if not Aeroquip does but I do not know their number. The minimum distance between center-lines is 2.5 inches which looks about right for this installation.

Bob Parry

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