Leak testing tanks ...

Post by **Spike** » Mon Jul 30, 2007 1:14 pm

Ive been testing my left tank for a month now

So the first time I put the tank under pressure, the balloon went limp pretty danged fast (a few hours). So I sprayed soapy water onto the rivets/seams/fittings and found a small leak. I fixed it, tightened the cap, vent line fittings etc.

I keep losing the balloon over time though. Thinking that it is a cheap balloon, I just did the test again yesterday with a "helium" quality balloon. As of this morning (17 hours after inflation) the balloon was still inflated.

Though it did lose 15% - 20% of its volume. So here is the question, is this something that you guys have seen? Am I being too picky?

Since my last fix I have at least twice sprayed every fitting, joint, seam, and rivet and found no leaks. I swear this thing is nice and tight, but dang it if that balloon doesn't get smaller over time.

Any thoughts?

Brantel · Post by **Brantel** » Mon Jul 30, 2007 1:54 pm

These test are very very very subject to temperature and differences in the atmospheric pressure from when you filled the tank with air.

As you found out, balloons are not created equal. Even the helium grade ones will leak over time. I used a manometer which is immune to that problem but not the AP and temperature issues. The best you can do is take a reading when the conditions are similar to what they were when you filled the tank.

Sounds like you do not have a problem now. Wait till it warms up, I bet that balloon will expand again.

tshort · Post by **tshort** » Mon Jul 30, 2007 4:16 pm

I did the manometer thing, too ... just got a long section of clear tubing from Lowes and filled it partway with water and pumped up the tank with a bike pump. I think Van's says 20" of water is the right pressure ... will have to check on that.
I made a pencil mark next to the level of the water, then whenever I thought about it for a few days I would make another mark and note the temp and barometer next to it. If I was smarter I could do some math to figure out where it should be, but I just waited until temp/pressure were similar to when I started and all was well.

T.

JohnR · Post by **JohnR** » Mon Jul 30, 2007 4:28 pm

Spike, the manometer is the way to go in my opinion. I tested both of mine at once and that way as long as they stayed in sync I figured I was good to go. The moved as can be seen in the photo but the levels stayed in sync so after 48 hours I figured it was good. Guess I'll find out in time.

By the way, a little food coloring makes the water much easier to see.

cnpeters · Post by **cnpeters** » Mon Jul 30, 2007 11:36 pm

I did both techniques - manometer on the first tank, then the balloon with the second when done. I had the same problem with the balloon after fixing an obvious leak - lost about 15% volume/24 hours. I sprayed soapy water everywhere - no leaks noted, so I did my victory lap.

Post by **Spike** » Mon Aug 06, 2007 9:05 am

Leak found. So, how do you find a leak when the balloon and soapy water dont help? Simple, put fuel into it.

Another builder and I put 5 gallons of AVGAS into my tank this weekend and sealed it off. 4 minutes later we found the location of the leak. It worked like a charm and the good news is that its in an easy place to get to. The vent fitting is leaking where it penetrates the end rib.

The nifty part of this test was that it was hot out and we were in the sun. About 4 minutes after we had put the cap back on, the evaporation in the tank pressurized it quite effectively. It helped to find the leak fairly quickly.

dons · Post by **dons** » Tue Aug 07, 2007 11:15 am

Now that is an elegant solution to a potential PITA problem.

smittysrv · Post by **smittysrv** » Tue Aug 07, 2007 1:30 pm

Which brings up a question. Do any of yous guys know of someone who put on their wings and then found out after putting in fuel for the first time that they had a leak? How big a pain in the bahootie was it to fix? No names need be mentioned.

Post by **Spike** » Tue Aug 07, 2007 1:52 pm

I don't, but the idea of pulling and reinstalling those tanks after the wing has been mounted is not one I care to entertain if. Blech ...

smittysrv · Post by **smittysrv** » Tue Aug 07, 2007 3:55 pm

I think you're right. My stomach just churns at the very thought.

JohnR · Post by **JohnR** » Tue Aug 07, 2007 5:04 pm

Nice furball Smitty.

Hope I'm not the one that needs to do that. It doesn't sound like much fun.

svanarts · Post by **svanarts** » Tue Aug 07, 2007 8:45 pm

smittysrv wrote:Which brings up a question. Do any of yous guys know of someone who put on their wings and then found out after putting in fuel for the first time that they had a leak? How big a pain in the bahootie was it to fix? No names need be mentioned.

Ahem. Well. Since names are not necessary I will tell you about a ... friend ... who just happened to build an RV-4 that looked just like mine. This.. friend... didn't test his tanks all that well. When he put fuel in his plane for the first time there were pretty blue stains on the bottom of the wing. Well, both wings actually. He had leaks in BOTH tanks. It was a pain but it only took him about half an hour to remove the tank.

Once the tank was removed he tried all the clever tricks that others told him about. One was mixing up some watery proseal and applying a slight vacuum to the tank to draw it into the leak. No dice. He tried putting green loc-tite on the leak and applying the same vacuum to the tank. No dice. He finally had to remove the access plate which had had fortunately NOT prosealed on. He only used fuel lube and it worked great. Anyway he took the plate off and was able to smear some proseal on the inside of the leak. That did the trick. The blue stains led him straight to the leak by the way.

He had to do the same with the other tank on the other wing but went straight to the proseal fix. I uh he hasn't had a leak since.

And yes, he had a LOT of fun.

cnpeters · Post by **cnpeters** » Tue Aug 07, 2007 11:39 pm

OK, now I'm paranoid! Maybe that mild balloon deflation on the second tank was significant, despite a negative soapy bubble test. I'll probably manometer test both of them soon when I do the aileron pushrods before closing the wing, and if ANY deviation beyond that compensated for by barometric change, I will pour in some mogas (or avgas) and check.

smittysrv · Post by **smittysrv** » Wed Aug 08, 2007 7:01 am

I'm glad now I watched the Orndorff video on prosealing the tanks. George really smmmmeeeeeeaaaarred it on thick, so I did the same. May the tank Gods be with us.

Brantel · Post by **Brantel** » Wed Aug 08, 2007 7:21 am

I used the theory of more is better on my tanks like George O...

I just did not see a reason to skimp on the sealant. I used 1 & 1/2 quart kits to get the job done. Hey it helps move the CG forward

Lots are jumping on the fay sealing method but I see that some of those guys have minor leaks at the end. It sure seems easier and cleaner but I did not want to risk it.

Post by **Spike** » Wed Aug 08, 2007 9:38 am

Very good points, but quantity does not guarantee success. I used a large amount and had a leak at the vent penetration. And I had used tons of proseal for that. Oh well, you live and you learn.

John

Brantel · Post by **Brantel** » Wed Aug 08, 2007 10:53 am

Spike wrote:Very good points, but quantity does not guarantee success. I used a large amount and had a leak at the vent penetration. And I had used tons of proseal for that. Oh well, you live and you learn.

John

Yep I think it is more luck than anything...

I say just make sure you clean very well with something really strong, do not leave any air pockets or voids, create fillets around everything inside and out, dab sealant over the rivet tails, don't move anything before the sealant sets and don't skimp with the sealant. This gives you a good chance of getting lucky.

JohnR · Post by **JohnR** » Wed Aug 08, 2007 9:22 pm

svanarts wrote:
Ahem. Well. Since names are not necessary I will tell you about a ... friend ... who just happened to build an RV-4 that looked just like mine. This.. friend... didn't test his tanks all that well. When he put fuel in his plane for the first time there were pretty blue stains on the bottom of the wing. Well, both wings actually. He had leaks in BOTH tanks. It was a pain but it only took him about half an hour to remove the tank.

So do you.. I mean does he plan on testing the next set better?

svanarts · Post by **svanarts** » Wed Aug 08, 2007 9:41 pm

JohnR wrote:
svanarts wrote:
Ahem. Well. Since names are not necessary I will tell you about a ... friend ... who just happened to build an RV-4 that looked just like mine. This.. friend... didn't test his tanks all that well. When he put fuel in his plane for the first time there were pretty blue stains on the bottom of the wing. Well, both wings actually. He had leaks in BOTH tanks. It was a pain but it only took him about half an hour to remove the tank.
So do you.. I mean does he plan on testing the next set better?

I'm going to watch over HIS shoulder and make sure he does it right this time!

1:1_Scale · Post by **1:1_Scale** » Thu Aug 09, 2007 9:39 am

I think you guys are being too picky. The SR-71 leaks fuel when it's on the ground, so I'm sure skin friction and expansion will seal your tanks up in the air, just like the SR

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