J

jdmunzell

Well Known Member
Hi all:

I know there are multiple threads dealing with this, but couldn't find exactly what I am asking.

I am about to close up the left fuel tank with the baffle, and wonder if I should route a fuel return line in there before I do. How big should the line and fitting be, and which bay should the line empty into? Also, should I be running these return lines into both tanks or just one of them? I don't know too much yet about the mechanics of FI systems, so I don't know if it is even possible to run the return line from the engine into a tee, with two lines coming out...one for each tank.:confused:

I don't know yet whether I will be going the FI route yet or carborated, but it seems smart to think about this now. I could always cap off the line if it doesn't get used.

Do some guys run a return line after the fact, and run it along the back side of the baffle and go into the bay of ones' choice?

What say you guys?
 
"Normal" FIs (Precision or AFP) don't require return to the tank. Obviously, neither does carb...

A fitting that doesn't exist can't leak.... so I'm not sure I'd be putting fittings around "just in case..."
 
Im putting them in mine for a few reasons... flexibility for one.. i plan on FI, but im not 100%. Resale... someone MAY want FI some day, and it will be one less thing to do. Sure they are one more hole to seal... but considering how many rivet holes and stuff that already penetrates the tanks... whats one more fitting??
 
return lines

ECI's mechanical fuel injection requires a return fuel line. I have built my fuel tanks with return lines with intentions of using the ECI fuel injection system that is basically like the original Continental fuel injection systems.

The lines are 1/4 inch aluminum lines. There are a few different ways you can run the lines. Mine ran through the Z-brackets on the rear baffles of each tank. They run all the way back to the last fuel bay in the tank and have a bulkhead fitting penetrating the rear baffle near the outboard end of each tank. Since I have built my tanks ECI has come up with a new configuration that simply has the return line penetrating the tank at the inboard round plate where the fuel pickup line and the fuel indicator are mounted.

ECI has some instructions, pictures, etc. Check them out here.
 
I did it

I think it's pretty easy to seal and cap a fluid fitting without much chance of it leaking. They are straight forward to seal.

I ran my return line in 3/8 because 1/4 would be too small and 5/16 was either difficult to find or more expensive. 3/8 is a little stiffer and therefore harder to work with. Come to think of it, I used some 3/8 and some 5/16, with a transition union, to make the bending easier in the tough areas and I had some 5/16 fittings anyway. Just not enough to do the whole job and didn't want to order them again.

I installed a dual Andair fuel valve (expensive) so that return fuel flows back to the tank it's being drawn from. The returned fuel dumps to the forward side of the first bay (on mine, others do it different) but If I were to do it again, I would go to the rear side of the second bay, on the bottom. Just easier and still gives the fuel some time to cool if it has received any heat during it's travel to the engine compartment.

If you are returning a significant amount of fuel (constant flow while flying) you really should return the fuel to the same tank that it is coming from. If you are just returning fuel from a purge valve prior to engine start it can go to either tank because it is very little. I think some people even return this to the feed line on the tank side of the pumps. Not sure. You cannot use a tee because that will allow both tanks to be connected and you will get fuel flowing between tanks. Very bad idea for lots of reasons.

At the time, I was planning to use the Egg Subaru package which required a return line (lots of return fuel). I have since changed my mind and plan on IO-360 possibly with fuel return (ECI). Even if I don't use it now, I'm still glad I installed it. It would be such a pain to add a return line later. The future of fuel types/systems is unknown. I'm trying to keep my options open. Keeping options open does add weight though.

Hopefully this helps. I'm not flying yet so this is NOT a proven design. Just what I did based on ideas and info available at the time.

Bevan
 
..understand about the problems with a tee. I like the idea of fuel going back to the tank it is being drawn from. It sounds like that dual Andair valve is a great way to accomplish that.

One question I have is about routing the line into the first or even second bay. Can I assume the fuel is being forced through the line and into a bay that is already full? Would the return fuel be forceful enough to force the other fuel back into another bay?
 
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