danielhv

danielhv

Well Known Member
I know some of you have filled with water, and marked clear tubing etc... and some have used air which changes with environmental conditions... I have access to nitrogen which is not near as sensitive to environmental conditions as air... anybody used nitrogen for tank testing? What psi did you test at?
 
Boyle's Law

Nitrogen expands and contracts just the same as air, if that is what you are referring to.
 
Don't over think this. The balloon and bicycle pump method worked great for me.

BTW, Van's does not recommend filling the tanks with water. Should you have a leak, you need to get all the water out before you can patch it.
 
Daniel.......I pressure tested mine with the cheap $5 kit from vans.....Pressurized the tank just enough to fill the balloon....sprayed it with soapy water. Let it sit over night....not much change....put it in the sun the next day and in under five minutes the balloon popped due to expansion.:D Good nuf for me. I know you have all the parts to do this cuz I ordered the exact same stuff as you.

Robb.....7A
 
If you have the tank in a non-temperature-stabilized area, you won't be able to see the difference between air and pure nitrogen with respect to expansion and contraction from thermal variation, so there is no reason to use the nitrogen there.

If you have it in a temperature-stabilized area, there won't BE any expansion or contraction from thermal variation, so there is no reason to use the nitrogen there.

The laws of gas behavior (Boyle, Charles, etc) do give some difference between pure gases (such as pure nitrogen) and mixes (such as atmospheric air), but the difference that you can see will be lost in the "noise" of thermal variation and atmospheric pressure changes. Don't try to reinvent the wheel.
 
n5lp said:
Nitrogen expands and contracts just the same as air, if that is what you are referring to.
Click to expand...

oh... :confused: I was under the impression nitrogen did not expand or contract as much as air... guess that rules that out!
 
airguy said:
If you have the tank in a non-temperature-stabilized area, you won't be able to see the difference between air and pure nitrogen with respect to expansion and contraction from thermal variation, so there is no reason to use the nitrogen there.

If you have it in a temperature-stabilized area, there won't BE any expansion or contraction from thermal variation, so there is no reason to use the nitrogen there.

The laws of gas behavior (Boyle, Charles, etc) do give some difference between pure gases (such as pure nitrogen) and mixes (such as atmospheric air), but the difference that you can see will be lost in the "noise" of thermal variation and atmospheric pressure changes. Don't try to reinvent the wheel.
Click to expand...


ah but the wheel is boring! lol... ok, ill just stick to the norm and use a baloon and bicycle pump. :D
 
1 or 2 psi air and a bottle of kid's bubble solution. Just slop it on the seams. When you don't find any leaks go outside and wave the bubble wand around for a few minutes. You'll feel so much younger <g>
 
danielhv said:
oh... :confused: I was under the impression nitrogen did not expand or contract as much as air... guess that rules that out!
Click to expand...

You mean - as quoted from the local tire shop, that promises you "more stable tire pressure"? That refers to the permeability of the rubber in the tire or tube. Oxygen molecules slip through the permeable rubber slightly faster than nitrogen molecules, with the end result that pure nitrogen in tires will leak out slightly slower than plain air. This, in combination with being extremely low water content and a non-flammable mixture, is the primary reason for nitrogen use in tires for aviation. The auto tire industry took that and ran with it with a borderline false-advertising marketing campaign.
 
soap bubbles

I used the balloon and bubble method. The balloon is the safety valve and not really the leak indicator. The soap solution is the key. Close visual inspection of ALL the rivets and seams for soap bubbles is what you want to do.
Note: It's hard to get the balloon to seal at the tank vent fitting. It's hard to get an airtight seal at the gas cap as soapy water makes duct tape come unstuck. Add more air and keep inspecting rivets and seams.
Clean the tank and perform the inspection a second time.
Steve
 
I live in the Mojave Desert and it is not uncommon for temp swings in one day of 30 deg or more. When I tested my tanks I used the Vans kit and clear tubes full of water. The way I made sure temp was not much of a factor was by taking the temp at start of test. Then the next day at about the same time I took the temp and waited until the temp was the same. I also kept the tanks away from the sun and in the same location.

http://www.mykitlog.com/users/display_log.php?user=alvarez&project=163&category=1710&log=47689&row=4
 
Fuel tanks and balloons

If you left the balloon on there for 24 hours or more and it contracted and expanded with the temp changes and Barometric pressure consistently and never deflated wouldn't that be sufficient to prove it wasn't leaking?
I had a balloon on my tank and it was filled up when I left it. Came back in the morning and it was deflated......came back in the afternoon (same time I started the day before) and it was inflated again back to normal.
I took that as a confirmation the tanks weren't leaking. This is on a composite Lancair tank however. No rivets.
 
I think lots of guys have used balloons to test, but it is pretty hard to get an accurate test with a balloon. With an manometer, you can mark the water level, and note the temp. Then you can come back 24 hours later and mark again, and note the temp again. It is possible to actually calculate if any pressure has been lost, but doing this over a few days gives you a pretty good feel for whether the tanks are leaking or not.

With a balloon, you have to kind of eyeball whether or not the pressure has gone down, and if so, then how much. I suppose you could get out the calipers, and get a little more accurate, but a balloon is not a perfect shape, so it is hard to calculate the volume to any level of accuracy. I suppose if you leave the balloon on for several days, you should get a good feel for whether the tanks are leaking or not, just not as accurate as a manometer.

Of course, you balloon guys do not have to deal with the problem where you go out in the shop 24 hours later, and all of your hose is lying on the floor because it got too hot and the glue on the duck tape melted and let every thing drop, so you have to use a whole bunch of duck tape to hold everything together for the next few days, so you can get an "accurate" reading. Everything has compromises.

Cheers,
Tracy.
 
Can't beat the laws of Physics

Edit: Should of read the whole thread before responding...I thought this was my chance to sound smart! :p

danielhv said:
oh... :confused: I was under the impression nitrogen did not expand or contract as much as air... guess that rules that out!
Click to expand...

Air is 78% nitrogen to begin with. But all gasses obey Boyles law which states that volume and pressure are proportional to temperature.

People like to put nitrogen in their car tires because nitrogen molecules are bigger than the molecules that make up the remaining 22% of air, so theoretically you won't need to refill your tires as often.
 
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Geekery

A datapoint just for fun:

Expensive laboratory leak detection apparatus use helium as the test gas because helium flows very quickly out of very small openings.

If you happen to moonlight as a clown and have a bottle of helium lying around, you could probably use it for a very fast and effective leak test, obviating the need to maintain pressure overnight. This way, temperature and pressure variations in the environment wouldn't matter.

M
 
tire shop

told me this once. I siad, well if i just keep topping it up with air after a while wont it be just nitrogen?? You should have seen their faces. Priceless!
:D:D:D


airguy said:
You mean - as quoted from the local tire shop, that promises you "more stable tire pressure"? That refers to the permeability of the rubber in the tire or tube. Oxygen molecules slip through the permeable rubber slightly faster than nitrogen molecules, with the end result that pure nitrogen in tires will leak out slightly slower than plain air. This, in combination with being extremely low water content and a non-flammable mixture, is the primary reason for nitrogen use in tires for aviation. The auto tire industry took that and ran with it with a borderline false-advertising marketing campaign.
Click to expand...
 
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