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  #11  
Old 02-10-2009, 01:43 PM
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Griff Griff is offline
 
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You are aware that "air" is about 78% nitrogen right?
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  #12  
Old 02-10-2009, 02:37 PM
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AltonD AltonD is offline
 
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Quote:
Originally Posted by Griff View Post
You are aware that "air" is about 78% nitrogen right?
I was gonna say that.
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  #13  
Old 02-10-2009, 02:38 PM
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frankh frankh is offline
 
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Default That 21% O2

Just messes everything up don't ya know...
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  #14  
Old 02-10-2009, 08:25 PM
gasman gasman is offline
 
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Location: Sonoma County
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Quote:
Originally Posted by Griff View Post
You are aware that "air" is about 78% nitrogen right?
NOT IN CALIFORNIA..........
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  #15  
Old 02-11-2009, 04:35 AM
RV10Man RV10Man is offline
 
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Location: Oklahoma City, OK
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Quote:
Originally Posted by gasman View Post
NOT IN CALIFORNIA..........
I'm an "OKIE" what is it?

Marshall
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  #16  
Old 02-11-2009, 09:26 AM
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AX-O AX-O is offline
 
Join Date: Jun 2005
Location: SoCal
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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/displa...og=47689&row=4
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  #17  
Old 02-11-2009, 11:33 AM
vonjet vonjet is offline
 
Join Date: Feb 2008
Location: Thousand Oaks, CA
Posts: 183
Default 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.
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  #18  
Old 02-11-2009, 11:47 AM
thallock thallock is offline
 
Join Date: Jan 2005
Location: Austin, Tx
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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.
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  #19  
Old 02-11-2009, 01:47 PM
jtrusso jtrusso is offline
 
Join Date: Apr 2006
Location: Santa Monica, CA
Posts: 325
Default 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!

Quote:
Originally Posted by danielhv View Post
oh... I was under the impression nitrogen did not expand or contract as much as air... guess that rules that out!
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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Last edited by jtrusso : 02-11-2009 at 01:51 PM. Reason: read the whole thread
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  #20  
Old 04-18-2011, 01:41 PM
foka4 foka4 is offline
 
Join Date: Jul 2009
Location: Ankeny, IA
Posts: 210
Default 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
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