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Fuel Tank - Fuel Return - Seemed like a good idea at the time

ERushing

Well Known Member
Looking for ideas. I'm hoping to avoid taking everything apart, removing the proseal and starting over.

I used an AN832-6D fitting and nut to make a fuel return inlet on both tanks (See page 5-33 of the builder's manual.) The fixed nut on the fitting is inside the tank. The fuel return is located right next to the vent fitting. Tightened up and pro-sealed and looked like it was going to work well. When it came time for leak testing, I threaded a cap on and tightened it down lightly. After spraying soapy water, I noticed a slow leak. When I went to tighten down the cap, the whole fitting started rotating. I hadn't thought about the fact that tightening the cap (or eventually the fuel return line) put force in the same direction as loosening the fitting.
E4BFAAC9-571F-4C79-ADAA-631B5A53365D_zps0xhcguuy.jpg


About the only thing I can think of is taking everything apart, removing the proseal, turning the fitting around and putting the fixed nut on the outside.

Any ideas?

Very disappointed. Sadly, apart from this small leak in the cap, the tanks are airtight.
 
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Eric, would it be easy to cut an access hole on the rear the tank so you can get you hand in there and turn the nut around? Then, just proseal up the new access hole. Just thinking out loud.....
 
There is a thread or two on getting in there through the fuel sender opening and using a modified wrench to tighten the nut but it sounds like you have pro-seal on the inside also so that may not work. Better to put in an access hole/cover on the real baffle and fixing it right as blueflyer mentioned..
 
I would recommend an access hole in the rear baffle then installing something (perhaps just a rivet, or a small plate and a rivet or two) that would prevent the nut from turning. If you put the nut outside you can end up with the exact same problem. What you should always do in a situation like this is put a wrench on the bulkhead fitting to hold it in place while installing a cap or a line. Then you are not putting any rotating force on the bulkhead fitting.
 
Thanks guys. Looks like I'll be cutting an access hole. Anyone know of a builder site of someone who's done this? It should be pretty straightforward... but adding a fuel return should have been straightforward too :)
 
Another take...

These horror stories were one of the main reasons I used a bung, riveted to the root rib, to facilitate my return line. With the bung, there are no fittings inside the tank that you ever need access to. Being riveted to the rib, there is no way for it to rotate, either. Works great, lasts a long time...
 
Van's anti rotation bracket would apply here.
My RV-8 fuel pick-up is a finger strainer fitting threaded into an aluminum plate riveted & prosealed into the aft bottom corner of the tank rib, similar idea to Rocketman1988's bung. The fuel return line is to the normal fuel supply fitting, without the tube inside the tank.
Perhaps you should review the plans and ad an anti rotation bracket to your return fitting. Just make sure the fitting is tight in the anti rotation bracket so it won't be moved enough to damage the Proseal when install/removing the vent line.
If that is too much bother inside the tank, Proseal & rivet on a bung to the rib exterior, using the same type blind pop rivets that are used to close the back of the tank, only perhaps longer if the bung & rib material is thicker?
Tomkk provided a link which has a nice pic of a different type anti rotation bracket, and a good background pic of a bung.
Polysulfide remover will lift proseal. I used some recently to repair an RV-4 fuel tank. Lots of hand work with scotchbrite pads and rinse water, but it does work, and new Proseal bonded to the old Proseal that had been retained.
 
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So here's the plan

I will cut an access panel in the rear baffle so I can get my hand and tools in there to remove the fitting and proseal. I'll clean the rest of the proseal off the tank and fitting and then evaluate as to whether I can fit the anti-rotation bracket shown earlier in this thread. I out the fitting very close to the top of the tank so this is somewhat in doubt. If not, I'll still rivet a flat piece of 1/8" sheet of maybe something shaped to fit two of the faces of the nut. Proseal between the bracket and tank. Proseal on the rivets and shop heads.

I will turn the fitting around putting the extended side inside the tank along with the nut. Proseal on the nut, proseal on the tank side of the fitting. Tighten to secure and let sit for a week. (Note that I want the fixed nut on the fitting outside the tank so that I can get a wrench on it when tightening or loosening caps and fuel return lines. That should alleviate most concerns about affecting the proseal while attaching fittings.)

Access panel will be circular cut with a fly cutter. 6-8 nutplates for #8 screws with countersunk rivets. Cut access panel plate to fit. Drill holes (prior to mounting nutplates on the tank, of course!) to match. Proseal on the access plate and on the allen-wrench keyed #8 screws. Tighten and let sit for a week.

Test for leaks. Cheer if no leaks and move on.... Cuss, throw things, threaten to quit, and then just fix the leaks if there are leaks.

Anyone see any holes in that plan. I'd REALLY like this to be the last work I do on the tanks!

For anyone who's interested, I'll document my work in case someone wants to leverage it later.

Thanks for everyone's help!
 
I will cut an access panel in the rear baffle so I can get my hand and tools in there to remove the fitting and proseal. I'll clean the rest of the proseal off the tank and fitting and then evaluate as to whether I can fit the anti-rotation bracket shown earlier in this thread. I out the fitting very close to the top of the tank so this is somewhat in doubt. If not, I'll still rivet a flat piece of 1/8" sheet of maybe something shaped to fit two of the faces of the nut. Proseal between the bracket and tank. Proseal on the rivets and shop heads.

I will turn the fitting around putting the extended side inside the tank along with the nut. Proseal on the nut, proseal on the tank side of the fitting. Tighten to secure and let sit for a week. (Note that I want the fixed nut on the fitting outside the tank so that I can get a wrench on it when tightening or loosening caps and fuel return lines. That should alleviate most concerns about affecting the proseal while attaching fittings.)

Access panel will be circular cut with a fly cutter. 6-8 nutplates for #8 screws with countersunk rivets. Cut access panel plate to fit. Drill holes (prior to mounting nutplates on the tank, of course!) to match. Proseal on the access plate and on the allen-wrench keyed #8 screws. Tighten and let sit for a week.

Test for leaks. Cheer if no leaks and move on.... Cuss, throw things, threaten to quit, and then just fix the leaks if there are leaks.

Anyone see any holes in that plan. I'd REALLY like this to be the last work I do on the tanks!

For anyone who's interested, I'll document my work in case someone wants to leverage it later.

Thanks for everyone's help!
I have had extensive experience repairing leaks on my tanks since my initial build (7 distinct different attempts to stop leaks on my left tank). I ultimately ended up with access plates in each bay on the rear baffle. Personally if this bulkhead fitting is on the inboard rib next to the pickup tube and such, I don't see why you would really need to cut an access hole in the rear baffle. The access plate on that end rib should give you plenty of access to anything within that first bay.

However, if you do go with an access plate, I would not use nut plates and screws to secure the access plate. Use sealed blind rivets. Vans has an access plate kit they sell for this very purpose. They supply all the rivets you will need. Have you contacted them in regards to the access plate? Your goal should be to never need inside that access plate again. Given that, the rivets in the kit are actually much better at sealing off the access plate than screws and nut plates would be. And trust me when I say, if you do have to get back into the access plate you will be able to drill out the rivets and get in. Been there done that! Again if you have not done so, call Vans and talk with them about the fuel tank repair kit.

Here is the link in their online catalog for the kit:
https://www.vansaircraft.com/cgi-bin/store.cgi?ident=1456938670-66-75&action=search

I have posted several threads on my experiences fixing fuel tank leaks. Here is one I started several years ago:
http://www.vansairforce.com/community/showthread.php?t=82929

Here is a search for fuel tank repairs. There is a lot of great advice in them:
http://www.vansairforce.com/community/search.php?searchid=26596538
 
Root Rib Access Plate

There is already an access plate in the root rib. The purpose of that access plate is to allow occasional access to the inside of the tank if ever needed.
BUT
So many people insist on ProSeal on that access plate, and that defeats the purpose of having a removable access plate. People say not to use the cork gasket with sealant, and use ProSeal instead.
Well, now you see why that's a bad idea.

I closed my tank access plates as they were intended: Use Permatex Hi-Tack or Permatex Aviation Form-A-Gasket sealant, applied to both sides of the cork gasket, and close it up. It won't leak. I've never had a fuel tank leak that was closed this way, on an airplane or a car.
The best part: Its very easy to open if you ever need to -- for situations like you have now.
 
Actually, on the 10, there is no access plate. There is a small hole for the fuel sender but it's about 3 fingers wide.

Thanks for the hint on the fuel tank repair kit and rivets!! I'll go that route.
 
Actually, on the 10, there is no access plate. There is a small hole for the fuel sender but it's about 3 fingers wide.

Thanks for the hint on the fuel tank repair kit and rivets!! I'll go that route.

Ah, sorry. All the previous models have an access plate that is about 5" in diameter. Soap-box lecture stands for those models, retracted for the -10.:)
 
Eric,

Why the return line? You won't need it on the 10 fuel installation if you are installing a stock system.

Vans has the tank repair kit.

Let me know if you need some eyeballs on your project... :eek:;)
 
Access hole in tanks to add capacitance plates?

Hello,

I am finishing up my empennage and about to move on to my QB wings and Fuselage. My wings were built in 2006. They currently do not have any fuel sender or capacitance plates in them. Vans says I can add the floats though the rib hole but I would like capacitance plates instead. I have read in threads that they are very accurate.

The question: Is it possible to add the plates to a QB wing? If possible, what is the best way. Is it through an access hole as mentioned in this thread?

Are capacitance plates worth this trouble?
Should I also add the option of a return line while I am in there?

Please post your opinions.

Thank you
 
The floats are amazingly accurate if you take the time to calibrate them. I am always within 1 gallon of actual at fill up. I never used the capacitive plates buy it seems they are a PITA for many.

If you want to add a purge valve to your IO-540 engine then a 1/4" return line is needed (but only on one tank). Be very careful on were you put it so that you do not create an interference problem when mounting the wings. You may want to first test fit the wings to see where to put this in. There has been a couple of threads on this so recommend you look them up.

I added a return line on my RV-10 (stock Van's IO-540) in case I wanted to back fit a purge valve. 310 hours now and I have no plans to do so.

Carl
 
Plates

I have the QB wings and was looking at the plates as well. I did not see any really good way to add them to the finished tanks. I ended up using capacitance senders from get avionics. In fact, they actually pre bent them for the -10, and they were installed in the stock location. People will say that they are not accurate when the tank is full because of the dihedral...true, however, the float which is in the same location is subject to the same error. More importantly, either is accurate in the lower range. I would rather know when I am approaching empty rather than full!:D
 
Hi Carl,

I completed the QB Tank mod this weekend to add floats and fuel returns to both tanks. At first glance, this seemed like a pretty easy mod (fuel return.) Looking back, I was a bit naive. Initially, I attempted to do it without putting in an access plate. I just drilled a hole near the fuel vent and installed an AN832-6D fitting. Unfortunately, I discovered that, without an anti-rotation bracket, it would rotate when tightening fittings.

If I had the ability to start over, I would still do it but:

1) I would just start by cutting an access hole in the rear baffle and use Vans fuel tank repair kit. (I did eventually anyway.) The access just makes things so much easier. I must have installed/ deinstalled each fuel sender a dozen time trying to get everything right looking through the vent hole and fuel feed hole. If I had the access hole it would have been a no-brainer - and eventually was.

41CAB3B8-FEDD-413C-84F0-C3FFEA718EF6_zpsgjj6z7mg.jpg


2) Pay close attention to the interior structure. I drilled my hole too close to a stiffener which made the anti-rotation bracket less than ideal.

AC185367-853A-434C-924F-C9772137D958_zps982dzrzh.jpg


The access plate results in a bit more proseal work but makes the whole process much easier.

If I could start over, I'd do 1 tank rather than 2, cut the access plate first, fabricate the anti-rotation bracket and then use it to locate the fuel return location in the same area I used. The outcome would have been nearly the same but I would have saved a great deal of time...

BFE2B0F9-6623-4619-8171-D54E0B309F45_zpss9e0uvls.jpg
 
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