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newbie tank pressure test questions

L

Lars

Well Known Member
Sponsor
First of all, yes, I've searched...

I have a -7 QB, currently working (very slowly) on the wings. I've seen plenty of references to pressure testing the wings using manometers. Seems easy enough, and I found the kit Vans sells with the shrader valve & AN cap on their website. What I can't find is any reference to tank testing in the instructions or the plans. Am I blind? OK, don't answer that- I suppose I must be. I couldn't find anything on this forum about pressuring testing QB tanks, but I presume the tanks should be removed from the wings to do the test?

I did find a thread that mentioned pressurizing the tanks to 24" of water, where did that number come from?

Thanks!
 
24"!?!?!

Just do the manometer trick that I'm sure you have seen on a 100 web sites. Van's kit is nice but you should have everything you need in your hardware now. with the exception of a few items from a harward store and a autoparts store.

Just flare the end of two 3" or so long aluminum tubes, one small one for the vent tube and one larger one for the fuel line. Using the AN fittings attach them to the vent and fuel supply fitting on the tank. Go to your favorite home improvment store get a short section of clear tube large enough to fit over the vent tube and a 5-6' long tube large enough to fit over the fuel supply tube. Using a small hose clamp, clamp each of them to the tank. Make a trip to your favorite autoparts store and get a rubber valve stem w/ schrader valve. The longer the better. Using a utility knife cut off the "grommet" end of the valve stem the is opposite the "valve" end. The end you just cut should fit into the clear tube you attached to the vent line. If it's a tight fit ou can heat up the clear tube to stretch it over the valve stem.

Now set up for the loop with the water trick (manometer). A little food coloring added to the water makes it easier to see whats going on.

Using a bicycle pump slowly pressurize your tank. DON"T USE YOUR AIR COMPRESSOR! I think 24" is way overkill. You'll be surprised how much the tank will groan with about 12-18". What ever you do don't let the water on the pressure side go past the bottom loop. If you do it will shoot the colored water surprisingly far accross your shop. don't ask :)

You can spray the tank down with some soapy water to look for some leaks.
 
24 inches is a lot

Thanks.

24" is almost one psi. Quite a bit considering the surface area of the tank. There's no way I'd use a shop compressor for that job. Good bye fuel tank. I'll try 12" or so.

Good point on the shrader valve. I've got an even easier idea- I'll grab a bicycle tube out of the box of leaky tubes (I accumulate them and patch a bunch at once) and just cut one out of the tube.

Now to get the inspection plates and senders pro-sealed into place...
 
Lars said:
I found the kit Vans sells with the shrader valve & AN cap on their website. What I can't find is any reference to tank testing in the instructions or the plans. Am I blind?
Click to expand...
Van's pressure test kit comes with instructions on how to set up the manometer and how much air to pump into your tank.
 
alpinelakespilot2000 said:
Van's pressure test kit comes with instructions on how to set up the manometer and how much air to pump into your tank.
Click to expand...

Got it. What they apparently don't do is mention testing in their plans. Good thing I spend time reading on this board! I would have wanted to test anyway- back in another life I built custom truck gas tanks at a welding shop. We used more than 24", not saying how much though.

On a tangent, I wonder if anyone has had problems with leaks in a QB tank? On mine at least it appears that they were quite generous with the Pro-Seal.
 
Just remember, when you read a manometer, read the total difference between both sides. IE: If one side raised 12 inches, then the other side fell 12 inches, for a total of 24 inches.

There was a post on here, don't remember where/when, but an engineer calculated the pressure on the tank from a vent line turned into the wind @ 200 knots. He came up with .92 PSI. That is about 24 inches.

just my opinion
 
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AltonD said:
Just remember, when you read a manometer, read the total difference between both sides. IE: If one side raised 12 inches, then the other side fell 12 inches, for a total of 24 inches.
Click to expand...

Interesting... I didn't think of that.
I followed Van's instructions (which I think say 2 feet 3 inches) and pumped one side up about 2 feet ... no leaks. I guess I put in more pressure than I thought! Glad nothing blew!

Thomas
 
AltonD said:
Just remember, when you read a manometer, read the total difference between both sides. IE: If one side raised 12 inches, then the other side fell 12 inches, for a total of 24 inches.

There was a post on here, don't remember where/when, but an engineer calculated the pressure on the tank from a vent line turned into the wind @ 200 knots. He came up with .92 PSI. That is about 24 inches.

just my opinion
Click to expand...

Thanks for all the advice!

That would be using Bernoulli's equation. Guess I should have thought of that myself (also a mechanical engineer, but rusty on the fluid mechanics). No worries on the manometer, I have made & used lots of them- though not on a fuel tank. I shall read carefully. I'm already suffering from tool lust again, having seen some pics of digital thermometers in other peoples' posts about this topic.

Any pointers on making sure the filler caps seal?
 
I have the "deluxe" caps ... all I had to do was put a thin film of Fuel Lube / EZ Turn on the gasket and neither one leaked...

T.
 
If it is leaking, spray some soapy water around it to make sure it is not the rivets. If not, put duct tape over the fuel cap and drive on.
I had a few bubbles on the center o-ring. It wasn't really anything to worry about; I just didn't want it to conceal any other construction leaks.

My fancy temp gage was a Sam's Atomic Clock.
http://www.mykitlog.com/users/display_log.php?user=AltonD&project=75&category=1262&log=17132&row=27

BTW, I wouldn't pro-seal the inspection cover just yet. If there is a leak (I had one on the BNC connector for the Cap probes), you will have to remove the cover. I just wasted the cork gasket and put some silicone sealer on it for the test. After that, chunk the cork gasket.
 
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hmmmm

well i can tell you they can take more than 24". i put the balloon on the vent and used the manometer (the balloon was my visual safety) and pressureize with my compressor untill the balloon started to inflate.(its a big tank) and left it overnight. if iirc vans says something like 1.6 psi i did not inflate the balloon very much and the tank looked like it was very pressureized. i wont mention how high the water coulmn was for fear of someone thinking i was setting the rule. but it was way higher that those listed . :eek:
yes i know 1 .6 psi can have a huge bursting force on a container this size.

NOTE: THIS IS WHAT I DID :eek: NOT SAYING YOU SHOULD :rolleyes: BUT I KNOW I READ IT SOMEWHERE :eek: GOD HAD MERCY ON THE FOOLISH and THE STUPID :eek:
 
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cytoxin said:
NOTE: THIS IS WHAT I DID :eek: NOT SAYING YOU SHOULD :rolleyes: BUT I KNOW I READ IT SOMEWHERE :eek: GOD HAD MERCY ON THE FOOLISH and THE STUPID :eek:
Click to expand...

I have never done anything stupid except for all the times I did something really dumb :eek:

I need one of those clocks. Come to think of it, that looks a lot like the alarm clock on my wife's side of the bed. Hmmmm...

Found EZ Turn on Aircraft Spruce's site. Yet another thing to order.

Good point on sacrificing the cork gasket- a good use for it. FWIW Pro Seal also works to seal automotive fuel senders on old trucks :D The cork gasket lasted until the first warm day when the tank heated up.
 
Sealing fuel caps

Was having trouble sealing mine with tape. Found someone who suggested the use of a balloon in the cap hole. Just blow up balloon in the hole; worked great!
 
vans info

found vans info on the pressure test today. 2.4psi which is a 6 feet above where hose enters the tank.....dont forget that balloon :rolleyes:
 
Most aluminum fuel tanks in the marine world are tested to 3 psi, but they are typicaly made of somewhat thicker aluminum.
 
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