Tank Leak Checks (again)

I was really excited when my tanks were pressured up for leak checks and with Snoop and soapy water no bubbles were observed at any seam or rivet. But I can't get the satisfaction of seeing the balloon stay up for a day or two like some people do. The reason is that I can't find a single way to seal up the fuel filler.

Tried two kinds of duct tape, a packing tape, glove over the cap, saran wrap over the cap and a baggie over the wrap. Three layers of duct tape each layer 90 degrees to the first gives the best performance.

BUT, has anyone made the RV-14 caps truly leak free for the test?

I suppose with good pressure in the tanks and no leaks away from the fuel cap I should just build on.... but it would be nice to get that 100% satisfaction!

Foil Tape will Do It

Hi Dudley, I had the same problem. I used a manometer so very slight
changes could be seen. I always had a slight leak down and water and soap
showed no leaks. I was using clear packing tape over the fill caps. I went
to Lowes plumbing dept and bought some Oakley Leak detect. Has the
fuzzy ball applicator on the top. Pumped us and wiped everything down and
nothing at first. Then fine bubbles started around the joints of the 3 layers
of packing tape at the fill caps. Friend told me to get some wide, cover the
cap in one pass, foil tape. Removed packing tape and cleaned around cap
with alcohol and applied the tape and used a flat stick to rub the tape down
on the skin around the cap. That did the trick. Pumped to 27" on the mano
and no bubbles anywhere. Held for two days with only slight variations
due to local pressure and temp.
Tanks have had 100LL in them for two months now, since move to airport,
and doing engine run in procedure, with no leaks.

I have found that the best way to test the tanks is to out them in flight attitude (dihedral) and fill them up with avgas. Make sure there is a vent line and that it is pointed up so fuel doesn't leak out onto your shop floor (as much as it would if it was pointed down) as it expands. Let it sit like that for a week. If there are leaks they will show up as blue stains.

Leaks around the caps aren't good because water will get in if it sits in the rain.

I tried the foil tape and got nowhere; but it was time to refresh the duct tape supply and I bought a big roll of Nashua 398-HVAC All-Weather duct tape. At first no joy.

So then I decided to play with the fuel cap. It seemed very loose, like the gasket on it would have no purpose. So I tightened the nut on the mechanism so that it would just close with a little extra margin, and now the cap fits much more securely and I think the gasket has some grip.

With just the cap I can press up to 12" on a manometer and it will hold although I didn't let it sit for hours. Higher pressure it leaked. So then I used my new duct tape and with that I can get it up to 27" and it is seeming to hold.

I have the cleanest tanks in the southeast if not the country. I've used an awful lot of soapy water and can't find a leak anywhere. If there is one it is too small to make bubbles with soapy water or Snoop.

Also, Snoop can be had for about $4 an 8 oz bottle if you go directly to your local Swagelok distributor. We have one right by the house here in Baton Rouge. Call ahead and setup your account for quick pickup. Snoop evaporates a lot more cleanly without the soap residue. And it makes really big bubbles if there is a leak.

If I still get a little seepage I'm tempted to go the hot tub route. I'm not wanting a lot of fuel in my shop..... and i'm not at the airport with it.

Try wide plastic (PVC) tape to seal the fuel cap area...

Like others, I had persistent leaks from one of the fuel filler caps. I tried various patterns of layering packing tape but the air (from a manometer) first bubbled the tape up over the cap, and then made its way through the seams in the tape, no matter the pattern or how many layers I tried (and I tried a few). Soapy water seemed to make it worse as it helped the tape lift (though it did confirm the leak path from the cap). I solved it by adjusting the filler cap, increasing the tension applied in locking it in place. Once the cap no longer leaked, the tape no longer leaked - in fact the tape probably wasn't even needed.

Heat

Even with proper venting, I've found rivets that weep when the temps are high and the tanks are full (summer in the hangar!). The weeping shows over time rather than immediately. I don't have a solution, as yet. But, the weeping appears spontaneously (I saw the fuel coming from the weep site and eye-ball spreading) and on occasion has stopped (all very mysterious!!).

I would suggest using Jesse's method and include a very hot hangar for several days or, perhaps, in the sun light (as if flying). Doesn't solve the problem, but may cause it to occur before the tanks are on the wings, which is a major hassle!

use a nitrile glove...

To completely seal the gas cap for leak testing you can use a nitrile glove placed in the opening under the cap.