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Fuel return lines. Don't make this mistake

Bluelabel

Well Known Member
So, last week, we discovered our first major BOO BOO....
In starting to plan for attaching the wings, we were noting how we wanted to connect the fuel lines, i.e. make a piece of tubing, get hoses made etc...
Since we are going with the EFII Fuel Injection, we off course need a full return line into the tanks since it runs much like an automotive loop. Our fuselage had the return lines already plumbed when we got it since he was gong to put a Subaru in it. So we just had to plan on it for the tanks.
As it turns out, we placed the return line to the tank right where it will be in the way of the main spar... OUCH!!!
How could we have done such a bonehead thing you ask? Well, return lines are not part of the plans and it was one of the first times we had to make a decision as to where something would go. We picked a spot far from he fuel pickup but somehow didn't account for the spar....
After sulking over it for 30 minutes feeling like an idiot, and looking up every known adapter and fitting in existence, we came to the conclusion that the only fix is to bite the bullet, cut into the tank at the end, remove the the bulkhead fitting from the inside (as it was put in), seal it up, put in a new one, then seal the tank back up.... not looking forward to it.
I've been having dreams (well nightmares) that the first time we put fuel into the tanks that, even though they passed all our tests, they for some reason are going to leak like a siv. Maybe my subconscious knew what we did.....


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The worst part.... 1/2" further out and we'd be fine.....
In the immortal words of Homer Simpson..."DOH!!"


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Man, I think I made the same mistake. Didn't even think about it. My return fitting is about 1 1/8" away from the wing spar, which I don't think is enough room to fit the front bulkhead spar in there and be able to thread a hose fitting on it. I may have to pull the bulkhead spar down from storage and just see.

Reading the plans, the thicker of the two fuselage spars goes towards the leading edge, correct?

Bummer. :(
 
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Hmmnnn...

Yup..... Guess I'm not the only one.....

Our tanks have been attached to the wings for almost a year.... Decided the best thing is to take them off and go in from the back... Nice clean hole that will be easier to get good seal on.
 
I'm thinking for those who need to fix this, would it be feasible to remove the fuel sender unit and get access through that hole? I know it's tight and would require small hands, but it'd save cutting a new hole in the tank.

I plan to remove the fittings this way and patch the wrongly placed hole from the outside. Then relocate the fitting. If planned out properly, I think I can accomplish it without too much extra work.

John, separate question but do you have a source for the electrical connectors you are using? They seem like a nice solution.

Thanks!
 
I'm thinking for those who need to fix this, would it be feasible to remove the fuel sender unit and get access through that hole? I know it's tight and would require small hands, but it'd save cutting a new hole in the tank.

I plan to remove the fittings this way and patch the wrongly placed hole from the outside. Then relocate the fitting. If planned out properly, I think I can accomplish it without too much extra work.

John, separate question but do you have a source for the electrical connectors you are using? They seem like a nice solution.

Thanks!



Wow looks like I am in the same boat. I installed the BNC connector for my capacitance fuel quantity indication system in the same location. I will have to see how the center wing spars fit. I am hoping they just clear. Or I will have to cut holes in the rear baffles and install new ones. Man what a pain.
 
Sticky for -10?

Seems like enough people have done this - could we add to a sticky list of gotchas?
Doing a search only showed an RV14 gotcha sticky.

In my build, I've used Tim Olsen's list considerably for the RV10, but think this might be good to add to VAF.
 
I'm thinking for those who need to fix this, would it be feasible to remove the fuel sender unit and get access through that hole? I know it's tight and would require small hands, but it'd save cutting a new hole in the tank.

I plan to remove the fittings this way and patch the wrongly placed hole from the outside. Then relocate the fitting. If planned out properly, I think I can accomplish it without too much extra work.

John, separate question but do you have a source for the electrical connectors you are using? They seem like a nice solution.

Thanks!

I don't think the hole where the Sender goes is big enough. Not even for a tiny hand....

As for the connectors... they are Weather Pak. I think I got them from a combo of Amazon and Waytekwire.com. They come in a combos of 2-3-4-6 and you can just get the pins for the right gauge wire. Combined with some heat shrink they work really good.
 
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Okay, I gave it a shot last night and am happy to report that with proper planning and plenty of patience, it is possible to remove the ill placed fitting through the fuel sender hole.

I removed the fuel sender being careful to not strip the screws since they had proseal on them. I then safety wired my adjustable wrench to the front spar so I wouldn't lose it forever in the tank. I preadjusted the wrench and snaked it in the tank. Using a magnet extension wand, I was able to manuever the wrench into place on both the tubing flare nut and the bulkhead nut. Then I just tipped the tank on end to get the nut and small length of tubing I had attached to the inside nipple.

All this took me about 30 minutes and tired out my two fingers that I was able to fit in the hole, but in my opinion better than cutting a hole in the tank.

Next step is to patch the original hole from the outside using some AD41H rivets and a small patch and then relocate the AN fitting towards the leading edge on the other side of the vent fitting.
 
I need school'd on fuel systems. I guess I didn't plan out my fuel system selection ahead of time and have been putting it off. (My QB wings are all sealed up.)

I'm wondering if it is possible to retrofit a fuel return to my tanks if I go with EFII. Does the return line need to be plumbed all the way to the outboard end of the tanks so that the fuel in the tank doesn't have pressure against the returning fuel, or does it have enough pressure to just dump it in at the inboard tank rib?

Sorry if this is a dumb question. :confused::)

P.S. I hope I'm not changing the subject too much on this topic. I just thought if it is possible to retro-fit, then I'm sort of in the same boat you guys are in except I dont have an existing interfering fitting/hole in my rib.

Thanks!
 
From talking to Robert at EFII (call him, he's extremely helpful), it doesn't need to go outboard in the tank. A lot of folks are just having the fitting dump into the first bay. I originally had mine going to the second bay just to help cooling the fuel down a bit, but others that are flying say they haven't had any issues.

If you plan ahead, I think you will be able to retrofit your tanks through the sender hole.
 
Retro fit...

You don't even need the sender hole. I have the QB wings and am going to use the EFII system. After discussing it with Robert, I ended up using an aluminum flange with 1/4" NPT threads.

Pick a location, carefully drill the center hole and rivet holes. I used grease in the flutes of the drill bit to capture the chips, along with a vacuum at the drill site.

Debur, ProSeal, and rivet using closed end rivets.

Now you have a 1/4" NPT tank bung that you can install any fitting necessary...
 
If you are really worried (paranoid) about cool fuel, fire sleeve the fuel lines through the tunnel. It can get really hot in there especially if the heater is on.
 
You don't even need the sender hole. I have the QB wings and am going to use the EFII system. After discussing it with Robert, I ended up using an aluminum flange with 1/4" NPT threads.

Pick a location, carefully drill the center hole and rivet holes. I used grease in the flutes of the drill bit to capture the chips, along with a vacuum at the drill site.

Debur, ProSeal, and rivet using closed end rivets.

Now you have a 1/4" NPT tank bung that you can install any fitting necessary...

Thanks. I like this method. And as long as there's no problem with the system pumping the return fuel into the first bay then it should work just fine. What I'm still confused about is if the return line is pressurized through another pump. It looks like maybe the EFII fuel pump is two pumps (1 for the fuel going to the engine and 1 for the fuel return line. Is this right?)
For example, would it have a problem overcoming any positive fuel pressure from a full fuel tank as it enters the tank.
 
The EFII pump is a dual pump system with one primary and one back up. Both have plenty of power to overcome any fuel in the tank if the return line is plumbed in somewhere below the fluid level. If really concerned, plumb in a one way check valve close to the tank, but don't think that's necessary.

The flange idea is another option and may be the way I go as well.
 
return

Just make sure that your return line is 3/8" with -6 fittings to match the supply. The EFII system is a full flow system, i.e. the return line needs to be able to flow as much as the supply line.

The location of the return to the tank is non critical, though he said to keep it several inches from the supply fitting.

I don't think there will be any issues with hot fuel in the tunnel as the EFII system continuously flows fuel from the tank and back to the tank.

It is a double electric pump, one primary and one backup...no mechanical pump on the engine.

Don't forget that you will need to use a duplex fuel selector valve...you need to switch the return lines as well as the supply lines. I used an Andair valve.
 
Parts to use

Can anyone help me out with what parts/fittings/tubing are needed for this? Do you just order an extra set of vent line parts from vans?
 
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Return lines

I think each application is going to be different depending on the system being used and personal preference. In my case, I am using the EFII fuel injection and ignition, so for the fuel system I used:

EFII double electric fuel pumps mounted in the tunnel

Two EFII pre filters mounted one under each seat

Andair duplex fuel selector valve and extension

EFII Pressure Regulator...mounted on firewall

Two 1/4" NPT aluminum flanges, one for each tank return

Closed end blind rivets for flange installation

Firewall bulkhead fitting

Tunnel bulkhead fittings

Fuselage bulkhead fittings

B Nuts and sleeves

5052 aluminum tube for lines

Adel clamps

And a substantial amount of time to fabricate the lines:eek:

If I did it again, I would probably just get Tom at TS Flightlines to make all the lines.
 
I think each application is going to be different depending on the system being used and personal preference. In my case, I am using the EFII fuel injection and ignition, so for the fuel system I used:

EFII double electric fuel pumps mounted in the tunnel

Two EFII pre filters mounted one under each seat

Andair duplex fuel selector valve and extension

EFII Pressure Regulator...mounted on firewall

Two 1/4" NPT aluminum flanges, one for each tank return

Closed end blind rivets for flange installation

Firewall bulkhead fitting

Tunnel bulkhead fittings

Fuselage bulkhead fittings

B Nuts and sleeves

5052 aluminum tube for lines

Adel clamps

And a substantial amount of time to fabricate the lines:eek:

If I did it again, I would probably just get Tom at TS Flightlines to make all the lines.

Thanks, right now my biggest concern is the fittings for the return lines to the tanks, I'll make other decisions a little later. I just didn't want to get the fuel tanks closed up and then find out there was something I missed. That's one of the frustrating things about this project is I almost feel like I need to have it all planned out from start to finish, just when I think I'm sailing along, bam have you thought about X. Owell, one rivet at a time.

Thanks,
Lynn
 
FYI, the VA-141 fuel pick up flanges are threaded such that they have be mounted from the inside of the tank. They will only fit through the sender hole with a bit of grinding and then you have to find a way to hold them in place with proseal while you rivet them. I found the standard AN bulkhead union to be easier. I'll post pics soon.
 
FYI, the VA-141 fuel pick up flanges are threaded such that they have be mounted from the inside of the tank. They will only fit through the sender hole with a bit of grinding and then you have to find a way to hold them in place with proseal while you rivet them. I found the standard AN bulkhead union to be easier. I'll post pics soon.

Pictures would be great, my tanks are still open so all options are on the table right now.

Lynn
 
Our Fix

So, we debated about the best way to fix this on our tanks. Taking the tanks off, going through the back baffle, attempting to do what Tim did and go through the fuel level sender hole. In the end, we decided to make a nice clean hole where it could be serviced if need be. Moved the return port, used sealed blind rivets, sealed the HECK out of everything and are about to retest for air tightness.
Hopefully this will be the end of it. it isn't super pretty, but no one will see it... except here....:D
Lesson Learned.

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I drilled a hole high, and forward, with the same cautionary vacuum and grease method. Then, I snaked a long piece of wire through the hole and out the fuel sender hole. I put all the "inside" fittings on the wire, and pulled them into the hole (already prosealed). A washer on the wire pulled the fittings in place. Attached the "outside" fittings, and waited for the proseal to dry. Pulled the wire & washer back out the fuel sender hole, and closed it up.
John
 
I was able to do the final test on my tanks tonight after finishing my modifications. Here's a picture of the right tank. The return line is the fitting closest to the leading edge. I also replaced the phillips head screws with socket head cap screws.
image1-1024x768.jpg
 
Tim - Quick Question

Resurrecting this old thread.

Tim - What fitting did you use for your return line? I'm planning to blatantly plagiarize your work!

Thanks!
 
For anyone interested I just took my senders out 2 days ago because the guy I bought the 1o from had return lines put right in the sender unit itself. I do not need the return lines so I ordered new senders and will be installing them Monday and then putting my wings on.
I think the way he did would work fine but it was interesting how he did it right in the face of the sender itself.
 
Stamper,

That's very clever. If you have an opportunity to take a photo of sender return setup, I'd love to see it.

Take care,
David
 
Eric,

Sorry never saw your post on this. Check out my build log, details are on there as is the missing picture.

The flange looks like the tank bung kit from SafeAir1 for their ER tanks. I put a set on mine just in case I ever wanted to add something down the road. It'd work well for a return line too.
 
Looks interesting, Tim! I would think you'd be better off with sealed blind rivets and pro-seal vs sheet metal screws and pro-seal.

Other than that, it looks great!

I ended up doing the same thing as you originally did and found the problem when I tried to tighten up a fitting when I was doing my leak test. I ended up making a custom anti-rotation bracket, opening up the rear baffle and re-installing the return fitting with the anti-rotation bracket. I used Van's fuel tank repair kit to seal everything back up. It was a bit of a pain but not too bad.

I would think that this new fitting from EFII would make that process a whole lot easier! No need for an anti rotation bracket!
 
One other question - Does anyone have any pics of their fuel line return routing, especially through the wing-root area?

I'm trying to decide where to drill the hole through the side skins so that I can mount the fuel return lines from the tunnel to the wing.

I've got my fuel return tank fitting about an inch or two forward of the fuel vent fitting.

Thanks!
 
An Earls Stat-o-Seal and an AN6 bulkhead fitting works well too. With some care, you can work it through the sender hole. No proseal mess to deal with.
 
One other question - Does anyone have any pics of their fuel line return routing, especially through the wing-root area?

I'm trying to decide where to drill the hole through the side skins so that I can mount the fuel return lines from the tunnel to the wing.

I've got my fuel return tank fitting about an inch or two forward of the fuel vent fitting.

Thanks!

Resurrecting this thread again - can anybody point me at some pictures of where their 3/8" return line exits the fuse and the pipe arrangement in the wing root ?

Many thanks

Andy
 
Why does Vans not offer this as an option for QB wings? Would make sense.
I mean they can offer a return line installed as an optional upgrade at a price.
 
Resurrecting this thread again - can anybody point me at some pictures of where their 3/8" return line exits the fuse and the pipe arrangement in the wing root ?

Many thanks

Andy

This is what I did based on researching through various posts. Use this with caution as I have yet to install the wings to the fuselage.

Steve

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Return line

There are photos and descriptions in my build log on this topic.

mykitlog.com

Search for Sunman, Indiana. I am the only one building here...
 
Here's a photo of the return fitting location on my RV10. Bulkhead fitting sealed with Earls Stat-o-seals on both sides.

 
Are they easy to retrofit on a quick build tank that is already sealed?


My wings were already built when I put my return fittings in. Unibit, vacuum cleaner through the sender hole with some 3/4 heater hose attached to grab the chips. Short wrench through the sender hole to grab the nut. Maybe took an hour to do both sides.
 
There are photos and descriptions in my build log on this topic.

mykitlog.com

Search for Sunman, Indiana. I am the only one building here...

Thanks Bob - good to get a view of this. Looks like your return line entered the fuse near the top of the wing root - do you have any dimensions for the locations or a picture of the location ?

Many thanks, Andy
 
***this if for a RV-7***

So I finished my first (right) tank and I installed a 1/4 in return line (the same as the fuel vent line). Im assuming this is no good or is it ok with a IO360?!

Is it possible to just plum the other tank (left) with a 3/8 fuel rerun line and only have fuel return to this tank? IE is it possible for the engine to draw fuel from the right tank but return the fuel to the left tank?

If thats possible i could away placard the aircraft to run first on the left tank so it doesn't overfill.
 
***this if for a RV-7***

So I finished my first (right) tank and I installed a 1/4 in return line (the same as the fuel vent line). Im assuming this is no good or is it ok with a IO360?!

Is it possible to just plum the other tank (left) with a 3/8 fuel rerun line and only have fuel return to this tank? IE is it possible for the engine to draw fuel from the right tank but return the fuel to the left tank?

If thats possible i could away placard the aircraft to run first on the left tank so it doesn't overfill.

You should return fuel to the selected tank. The return flow at idle is around 99% or about 1 gal/min. The 1/4 inch return is probably ok if you avoid a lot of 90 degree fittings on the way to it.
 
Sanity check

Ok, so I'm building my tanks currently and planning to add a return line as I'm planning on an EFII solution. (Figure I can cap it off if I change my mind later).

I'm pretty clear on where I need to put the return line (or where I shouldn't), but starting to doubt myself on how I'm putting it in. Currently I have an order into vans for two more of the VA-141 fuel flanges. My assumption is if the fuel supply is the same size as the return, all is good? A few posts in this thread are making me doubt myself. (maybe I misread and the concern was how to attach a VA-141 once the tank is sealed since it has to go on the inside?)

Any issues with putting two VA-141 flanges on the tank. One for fuel feed, one for return?
If I go with a AN bulkhead fitting (-6 or do I need larger?) I would need to make an anti-rotation plate for the inside of the tank, right?

Sorry for the possibly silly question.
-----
Nevermind, looks like using another Fuel Flange (VA-141) and an AN816-6-6D Nipple should work just fine. At least that's what I'm doing for now.
 
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