How to: Vapor Return Lines in fuel tanks

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captain_john
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How to: Vapor Return Lines in fuel tanks

Post by captain_john »

Hi All, I am putting this together for several reasons.

1) I haven't found anyplace on the web where someone assembled a "How To" in a place that is open to commentary and allows us to work collaboratively.

2) I have been asked by a few people now to do this.

3) I am an educator and I like helping people out, even if I am wrong!

:wink:

I am not saying that my method is right! By all means no! It may not be, but I am willing to stake my life on it! You may stake yours on it too?

First, what is vaor return? I understand it to be the excess fuel that is delivered to the firewall forward area when the throttle is pulled back after a high flow situation. There is also a certain amount of fuel residing there at all times, even when you have pulled mixture to idle cutoff.

The EFI system sends this fuel back to the tanks for recycling.

Some peole have reintroduced this fuel/vapor mix back into the fuel feed line just after the tank selector valve with good results. I chose to return it back to the tank for cooling and mixing with the bulk supply.

Others have just dumped it overboard. I personally have cost, environmental and safety concerns with this method.

The Eci EFI system (which is't yet available) and the auto conversions need a Vapor Return (VR) system to work properly.

Eci had a nice .pdf outlining the components of their fuelie system, but I cannot seem to locate it right now. If anyone has a copy of it, please let me know. We can post it here.

In addition to the extra work of the VR lines you will need a duplex fuel selector from Andair like this one:

Image

I have noticed that no one seems to be giving these away at halloween or for Christmas near me, so be prepared... they are the better part of $600!

:o

With cost not being an object, this shouldn't be a problem!

Anywhooooo, you will need to get some additional 1/8" elbows for this job. I installed mine like this:

Image...so they would clear the capacitive sender plates.

The bottom one is for the VR line. This is what it looks like from the inside:

Image

You can see the nipples sticking into the first bay. (hahaha, I said NIPPLES! Sophomoric humor, I am good for that!)

I saved the root rib for last, so I could insert the tubes into position, rivet the rib and then tighen the fittings... in that order.

Image

This is the view of the left hand tank, second rib as the tubes pass through the rib. I kept the vent line OEM and ran the VR just below and to the rear of it. The flop tube is totally clear of it.

Image

... through the next bay:

Image

...and the next one too, until it reaches the center of the tank:

Image

...where I abruptly end it. Here it will dump into the center of the bulk supply for mixing and shouldn't affect the total capacitance read by the senders, as it should have minimal effect on the dielectric of the total quantity.

What do you guys think? Did I do OK? Anything to add?

I threw the poll on here for $h!+$ and giggles!

I am happy with the product! Hopefully it won't leak!!!

:drink: CJ
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It's all over but the flying! 800+ hours in only 3 years!

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captain_john
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Post by captain_john »

Oh yah...

See also the thread I posted on VAF before I had any information to go on:

http://www.vansairforce.com/community/s ... eturn+line

...and I am the one who voted with the first disparaging comment!

:wink: CJ
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greylingr
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Post by greylingr »

Thanks John
Rudi Greyling, South Africa, RV7 Tip-up, Current Status: Wings.
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Post by captain_john »

You are welcome, Rudi!

I do hope it is helpful to you!

Feel free to ask questions.

:) CJ
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Post by RV7Factory »

Great stuff CJ... Very useful!!!

That link you are looking for moved. Here is the new URL...
http://www.eci2fly.com/pdf/FIS11x17.pdf

Cheers,
Brad
www.RV7Factory.com

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Post by captain_john »

That's the stuff! Thanks Brad!!!

:wink: CJ
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Post by Spike »

Thanx Guys. I put some links to this and some of ECI's other great resources in the Document Share.

-- Spike
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greylingr
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Post by greylingr »

HI John,

Looks like you used AN-4D fittings for the vapour return, just like the vent. The main fuel line is AN-6D from the tank.
1) Do you foresee any problems in going from bigger to smaller?
2) Looks like the Fuel selector has AN-4D and -6D fittings?
3) Otherwise how are you going to reduce from -6D to -4D.

Thanks
Rudi
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Web Page: www.freepgs.com/flyboy
"Science, freedom, beauty, adventure...what more could you ask of life? Aviation offers it all" - Charles A. Lindbergh

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Post by captain_john »

Rudi,

I chose to go with the -4 sized fittings because I just don't think there will be that much fluid returning to the tank. I am making a guess, but if I am correct the vapor will "burp" fairly fast back to the tank. This shouldn't require a line as large as the feed as some fuel will be consumed in the process. Besides, issues normally arise (and are feared the most due to long ground operations) on takeoff where fuel consumption is at a high rate.

The Andair FS 20-20 D2 has -6 feeds and returns. If I were to do it today, I would run a -6 back to the selector and neck it down either at the tank or at the selector on the tank side. In my estimation, this system is far superior than not having a system at all and should prove to be reliable.

Also, there is a nice article in the 24 years of... where they discuss the use of Mogas and the use of Vapor Return lines. Good reading if you have the book. If not you need this book!

8) CJ
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It's all over but the flying! 800+ hours in only 3 years!

greylingr
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Post by greylingr »

Thanks John,

I have to book, but did not see the article yet, will look tonight!

Regards
Rudi
Rudi Greyling, South Africa, RV7 Tip-up, Current Status: Wings.
Web Page: www.freepgs.com/flyboy
"Science, freedom, beauty, adventure...what more could you ask of life? Aviation offers it all" - Charles A. Lindbergh

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Post by captain_john »

TTT

Once again for renewed interest gathered from other sites and for new readers of this forum.

Update:

In thinking about the utility of this modification, I am not sure that I will immediately make use of both return lines. If I were to do this today, I would plumb one and leave the other plugged. This would mandate operation from the plumbed tank until sufficiently depleted to switch to the other tank.

My reason for doing this now is to not disallow use of let's say an ECI fuel injection system and to keep my options open to engines of the future. Engine technology is on the verge of delivering significant improvements to us and when a good one comes along, I want to be able to evaluate it.

:) CJ
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Post by svanarts »

I'm not going to FI my engine but the thread was interesting nonetheless.

It's also good to see our South African movie maker on the forum. Welcome Rudi!
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Dan A
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Post by Dan A »

Don't really know why you guys are going with Air performance injection systems. I used the Precision Air Silver Eagle, the non certified version of the Bendex RSA, and I only had to run one fuel line. No return lines. After 135 hrs, it runs perfect! 8)
Dan

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Post by jim_geo »

I'm with ya Dan. Seems like a good system to me.

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Post by captain_john »

I gotta say that I am on the fence.

I like the fact that AP is on the east coast and I can run down there and do the balancing class real easy!

They want you to bring your own plane and work on it there!

I am real cool with that!

8) CJ
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It's all over but the flying! 800+ hours in only 3 years!

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svanarts
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Post by svanarts »

Way to go CJ! You made the top center headline above the fold on the RV Builder's Hotline! :yay:
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Post by captain_john »

WOW! I are somebody now!!!

I tells ya, I would gladly give up all this fame for just a few million dollars!

:lol: CJ
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Post by svanarts »

I bet you'll even be in the phone book soon!
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Post by captain_john »

Nawwww, no phone book for me!

STEALTH MODE!!!

8) CJ
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It's all over but the flying! 800+ hours in only 3 years!

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Post by jim_geo »

CJ how important do you feel it is to return vapor to the outboard end of the tank?

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