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Fuel Tank Vent Leak

azcloudflyer

Active Member
At about 28 hrs into Phase I flight testing, I noticed that I was dripping fuel from the right wing fuel tank vent. It was too consistent of a drip to be anything but a leak. The leak was coming directly out of the vent, not around it. The RV-10 vent system runs the vent pipe from the high side of the tank, through the fuel, to a bulkhead fitting at the lower inboard end of the tank. This fitting is submerged in fuel whenever the tank has 22 gallons or more of fuel. Within the wing root, there is just a pipe that you add to exit to the bottom of the wing and complete the vent system. I've concluded that the leak is at the flared tube to bulkhead fitting inside the tank. This fitting is not accessible once the tank is completely riveted together.

There is a 1.5" diameter hole for the fuel sender located about 3.7" away from the vent bulkhead fitting which is shown in the first photo. You can just barely touch the internal nut with your middle finger from this hole. My first step in developing a tool to go in the hole and turn the nut was to make a mock up of the fuel sender hole and vent position. The mock up is in the second photo below. Then with another engineer's expert help, we developed a tool that could go in the hole and swing far enough past the hole in each direction to turn the nut. You have to be able to swing the wrench far enough so that it can be repositioned back enough to pick up another flat of the nut. I was able to practice placing the tool on the nut using the mock up.

I flew off the right fuel tank as far as I could in flight. Then on the ground I transferred the remaining fuel from the right to left tank. I was able to go in and tighten the nut at least one and a half flats of the nut. It seemed pretty tight to me so I reinstalled the fuel float sensor, buttoned everything up and filled the tank with fuel. I wish the story ended here but the fitting continued to leak. It has slowed but the vent was still wet to the touch at the output end.

I decided to give it another try, so I flew off the fuel, transferred remaining fuel, removed all the cover panels and the fuel float sensor and tightened the fitting as much as I could using the tool. It seems really tight to me now and I don't think going any tighter could possibly be productive. Well it looks like that did the trick. It has stopped leaking. yeah! If this doesn't hold up I plan on removing the tank, capping the existing vent, and installing a new always dry vent at the outboard end of the tank. There is almost 2" of room between the outboard end of the tank and the next wing rib to add a bulkhead 90 degree fitting and vent tube there.

So my reason for posting this, besides relating my tale of woe, was to offer the use of this tool to anyone else that may discover the same problem with their quick build wing. But from my research in the archive this doesn't appear to be a common problem.

Back to flight testing.......


View of fuel tank rib
IMG_0915_t.jpg


Mock up of rib
IMG_0925_t.jpg


The right Tool for the job
IMG_0922_t.jpg


Internal fuel tank view of tool in use
IMG_0924_t.jpg
 
Very impressive!

That is quite an impressive accomplishment.
Hope I won't need to do that, all my fittings inside the wingtank are sealed in proseal.
 
sounds like--

the nut wasnt secured enough originally. Maybe we should rethink the fuel tank vent system?
Tom
 
Very cool!!

I saw the similar symptoms with my QB tank, so I figured I had a leak. As a hail-mary before attempting a repair, I blew some compressed air into the vent (with the fuel cap off, of course). The leak stopped and hasn't returned since.

-Rob
 
You still have one more trick to try, if it leaks again

Mike
Very impressive engineering. "If" that leak returns, you can try adding a copper SECO sealing washer between the flare and the fitting. They are designed for just this sort of problem. Very handy. You can get them from a lot of different sources. Aircraft Spruce carries them, but they are hard to find using the search feature. I've provided several links for this product. See

http://www.pegasusautoracing.com/productselection1.asp?Product=3202

FYI, Pegasus is owned by Chris Heitman, who built an RV-9A

http://lastminutemall.com/secoseals/SECO_7_Copper_Seals.html

http://www.flaretite.com/flaretite.php

For Aircraft Spruce, do a search for:

04-05004 DEL FITTING SEAL 1/4" OD

Charlie Kuss
 
I think those crush washers are a handy thing to have around. Especially when you have a steel-to-steel fitting that won't seal.

There could be a flaw in the vent flared pipe to fitting interface that the DEL Fitting would help with. To insert it, I would have to remove the nut and then manipulate the DEL fitting into place.

At first I wanted to inspect the flare with a bore scope. So I tried removing the nut on the mock up to practice. I was able to remove the nut with the tool but could not get the nut restarted on the fitting. The nut needs to be pressed onto the fitting at the same time it is turned and then not disturbed when you reposition the wrench. So after practicing on the mock up I was not confident I could get the nut back on if I took it completely off.

Maybe if I knew a basketball player that could start the nut with one finger for me via the fuel sender hole and then I could finish tightening with the wrench.

Mike
 
That is quite an impressive accomplishment.
Hope I won't need to do that, all my fittings inside the wingtank are sealed in proseal.

It sure looks like you could figure a way to swab it with proseal next. And the above should be standard during construction.
 
Left wing fuel vent leak

We recently purchased an RV10 (0ct 2012). We have exactly the problem that you discussed, only the left wing fuel vent. We had decided that the problem must be as you concluded, and were at a loss on how to tighten the nut in the fuel tank. It has been awhile since your posting. Do you still have the tool? Would we need the mirror image of the tool to use on the left wing? At any rate, your description and pictures should help. Thanks.
 
... If this doesn't hold up I plan on removing the tank, capping the existing vent, and installing a new always dry vent at the outboard end of the tank. There is almost 2" of room between the outboard end of the tank and the next wing rib to add a bulkhead 90 degree fitting and vent tube there. ...

I know this is an older post, but in case anyone is currently considering this, think carefully before relocating the vent to the outboard end. One of the reasons the vent is routed to the inboard end is to minimize the possibility of running fuel overboard in the event the aircraft is parked on a slope with a wingtip down.
 
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Why not do the RV-10 tank vents like the RV-6?

The RV 6 tank vents have never leaked on my plane. Why was the -10 designed the way it was?
 
I hate to bring this old thread to life, but my -10 has developed a leak in the right tank vent line. The wings were quick built. It appears that the interior vent fitting nut is loose.

The tank was filled completely when I did my fuel tank level calibration, but I did not see it then. After the first two flights, the tank vent is leaking. The tank is at about 20 gallons so the only two possibilities are a hole in the tubing or the "B" nut has loosened up.

Called Vans and Sterling came up with this thread. Not only that, he is going to fabricate a tool like the one in the first post and send it to me. After I use it, I will send it back to Vans and they will have it in case the issue comes up again.

Won't stop the flight test program, I can put a plug in the vent when on the ground an loosen the filler cap. Will report the results in a few days. I have to miss a couple of days of testing for another reason.
 
And do what to it when you are test flying?

Left out, will remove the plug and put in the fuel filler cap. Will leak slightly while flying, but is not an issue.

Charlie ... That was my immediate reaction, but I will try the tool and see if I can avoid taking the tank off the wing. I think they ought to have the QB factory proseal the fitting. Then they would more than likely check to see if it is tight, so you get a double fix. When I was a Nuclear Power Plant manager, that nut would be a specific line check in the Q.C. program.
 
Build it yourself

Hi Bruce,

I had exactly the same issue, I built the tool myself in the most basic form and it worked well to tighten the nut. It takes some tries to really catch the nut and you might only be able to turn it a bit by each attempt but all together I was done in 4 hours if I recall correctly.
If you stay below 20 gal it shouldn't be a problem.

Good luck
Michael
 
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Charlie ... That was my immediate reaction, but I will try the tool and see if I can avoid taking the tank off the wing. I think they ought to have the QB factory proseal the fitting. Then they would more than likely check to see if it is tight, so you get a double fix. When I was a Nuclear Power Plant manager, that nut would be a specific line check in the Q.C. program.

In my case, I had prosealed the nut as well, but it wasn't quite enough to counteract the loose nut. Admittedly if I had either tightened MORE or added MORE proseal the issue wouldn't have happened.
 
Alternate approach

I had a similar problem with a dripping vent in my 10's QB tanks. I tried a different approach, and poured quite a bit of that green locktite (forget the number) used in fixing weeping tank rivets through the vent line with the line inverted, lightly blowing through it to keep it from pooling and blocking the line until it had dried (which isn't but a few minutes), then flipped the vent back to normal to further ensure it drained any excess. Fixed it, no issues since.

Dwight
 
I finished the repair today (I hope). Mark, you were dead on, I could have removed the tank, punched the hole in the back and had it back together in about half the time.

Ended up with three cut down wrenches, all with different clocking. Put one on (not easy) and pushed it with my thumb as far as possible. Then remove the wrench (not easy when using the modified box wrench). Then put the wrench just used on the mockup and move it to its end position to set the mockup nut to its current clocking. Now check on the mockup which wrench will have its handle in the hole in the tank and repeat again.

It took about 1.5 turns to get the nut tight, about 1/6 turns per hour! I thought the seat support bracket was bad!

The nut was hard to turn at the start, just like a tube nut where things are not lined up.
 
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I found it took me less than 2 hours to remove the tank, cut a hole in the bulkhead, tighten the B-Nut, apply some proseal and seal the tank back up. If you use the B 1/2 Proseal (http://www.vansaircraft.com/cgi-bin/store.cgi?ident=1393521243-438-180&browse=misc&product=proseal), it has a 30 minute working time and was completely cured in 24 hours. I waited 48 just in case. A much smaller issue than I had feared. Just be sure to clean out all the debris from cutting the hole.

You removed the tank and did all that in less than 2 hours? I just pulled the tanks on an RV-10 the other day and it took more than 2 hours just to pull the 24 bolts holding the tank to the spar, much less removing all of the screws or doing any cutting or prosealing.
 
Yup, the first time I had to remove a tank it took quote a while. The second time (in prep for painting) muscle memory was already in place and the bolts were easy to find and remove. I found using a ratcheting wrench was much faster than using a ratcheting socket for removing the bolts.
 
Do you think an open ended ratchet wrench would function better than the standard wrench. This way there would be no need to pull and reset the wrench with each turn.
 
Yes, but do they exist? You have to be able to get it over the tube.

I filled the tank today and the vent did not leak.
 
Yes, I googles searched it and Sears along with others have them. Its an opened ended ratchet type wrench. What size wrench worked on the nut. I have the quick built wings so before I get to them Im going to try and tighten those nuts before installation.


Yes, but do they exist? You have to be able to get it over the tube.

I filled the tank today and the vent did not leak.
 
Ok, iI actually have a set of them. I checked the stroke required and it was too great to use in the 1.5" hole in the rib.

I wouldn't bother checking your QB wings, mine was a rare occurrence. If anyone has an issue, I would recommend taking the tank off and going thru the back, Vans has a kit to get into tanks because of the "slosh" issue a few years ago. They are regularly used when a builder has a stubborn leak.
 
I was here 4/24/15
upload_-1

Any dimensional drawings of this tool, Weasel? Do you have it available for loan - or anyone know if Vans has one?

I have the weeping right fuel vent issue above 2/3 full and it looks like I may need to quit ignoring it and tackle it head-on. I've been keeping the right tank drawn down below 2/3 until just before flight. Kinda works - but kinda half-a$$ed approach.

I haven't yet tried the green LocTite gargle mentioned above, and it seems worth a try first.

I'd hate to pull a tank, but ultimately, you do what you have to do... Is this wrench method through the fuel level sender hole less time and effort than pulling the tank and cutting the access hole in the rear baffle?
 
Proseal joints

Just my 2 cents... right or wrong...

Whenever I build tanks, every possible fuel escape point is sealed with ample proseal, including all the internal tank fittings and unions. I flare and assemble the vent line as per the manual, and then completely encase the whole fitting and half an inch of the tube in a generous coating of proseal just to be sure.

Due to my affinity with proseal, the tanks I have personally built have never leaked. However, I got a set of QB tanks from Vans a few years ago, and they leaked from day 1. I tried all the fixes short of cutting the tanks open, but todate, they are still seeping from some of the rivets on the top and bottom of the tank, where the paint is bubbled directly over the rivet head.

Proseal is your friend. Dont be afraid to use a lot of it to make sure the fuel stays in the tank, where it belongs !!!
 
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