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Dave's RV-7A Builder's Log
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Date:  5-3-2015
Number of Hours:  5.00
Manual Reference:  
Brief Description:  Fuel system plumbing

Had I known going in that I was going to need five hours, about 8’ of tubing, and an extreme amount of patience to plumb the last four inches of the fuel system, I would have stayed home. I arrived at the hangar with the thought that I would knock that out in one try and move on to the brake lines. In the end, I got it done, but there was a time where I was convinced that I would return home in defeat.

The plans call for the filter to be attached directly to the input side of the pump. This assembly, and the location of the pump in order to fit under the dog house cover, leaves the input side of the filter almost directly under the outlet of the fuel selector—and only about 3 ½” below it. The plans show a nice “J” shaped bend attaching the two, but it turns out that nice drawings do not always translate to something actually physically possible. The key issue at hand here is bend radius. Any tubing has a minimum radius that it can attain without kinking. A tubing bender (at least mine) is designed to bend only slightly more than 90 degrees, but this particular bend required about 135 degrees to make the turn. To complicate this, while I figured out a way to get the requisite bend without kinks after about five or six attempts, I ended up with the bend too close to the ends to allow the ferrule to slide on far enough to flare. Unfortunately, I was chewing through my supply at an alarming rate.

At this point I had transitioned to an idea where instead of making a straight bend, I would allow the tubing to drop down below the filter, gently sweep around to make a 360 degree turn, and then back to the filter. This required about an hour’s worth of very gentle bending, checking progress, bending some more, and then final adjustments until the ends matched up. The picture is proof--fuel system is plumbed!
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Pump to firewall run

Pump to firewall run

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Attempt #19...still some interference with the side

Attempt #19...still some interference with the side

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This is going to have to do it...almost out of tubing...

This is going to have to do it...almost out of tubing...

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