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  #11  
Old 03-29-2008, 02:34 PM
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I've never flown with O2, but I thought that aviation (and medical) oxygen was dehumdified to prevent potential condensation freezing in the lines and cutting off the O2, and that welding oxygen was not which made it dangerous to use for breathing at altitude.

Is that just an urban myth?
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  #12  
Old 03-29-2008, 04:57 PM
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They all come out of the same big tank.
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  #13  
Old 03-29-2008, 05:19 PM
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As a certified welder, I can say that without quetion welding gasses are is good if not better than anything else. Lets say a batch of medical grade o2 gets contaminated with a tiny bit of nitrogen or CO2 or moisture...it is not going to be noticed by anyone who is brething it. When people are administered O2, it always mixes with the ambient air, you could never tell a tiny bit of impurities (assuming it not poison or something.) Welding gasses on the other hand, tiny amounts of impuritys get noticed in the weld color, weldability, arc behavior, etc. The real difference in Medical and Weld grade O2? The Medical tanks gets the fancy chrome valves
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  #14  
Old 03-29-2008, 06:23 PM
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Quote:
Originally Posted by Auburntsts View Post
I've never flown with O2, but I thought that aviation (and medical) oxygen was dehumdified to prevent potential condensation freezing in the lines and cutting off the O2, and that welding oxygen was not which made it dangerous to use for breathing at altitude.

Is that just an urban myth?
It used to be based in some fact, but those days are long gone. All oxygen now sold in bulk is produced through air liquefaction, which requires removing all the moisture and carbon dioxide from atmospheric air before compressing and chilling the resulting air stream to -300 F at about 200 psi, where the oxygen and nitrogen (99+% of whats left in the air stream at that point) will liquify and this resulting fluid is sent to the fractional distillation tower (a supercold version of an alcohol still apparatus) to separate the oxygen from the nitrogen. The purified streams are then reliquified and stored for bulk sale. It all comes out of the same tap.
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  #15  
Old 03-29-2008, 06:50 PM
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Cool, thanks for the info guys!
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  #16  
Old 03-29-2008, 07:04 PM
Norman CYYJ Norman CYYJ is offline
 
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I ask the local o2 supplier what the dew point was of medical o2. He said it was -60c. I figured that I was safe. I won't be flying in those temps and if I am o2 won't be on my mind. You can quite often find good used medical regulators on e-bay. If you do go the medical route rent a regulator used on small children. You can get the flow rates down quite a bit more than the standard regulator.
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  #17  
Old 03-29-2008, 07:18 PM
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Norman,

I use liquid N2 (occasionally O2) extensively in my lab at work and would be extremely surprised if the O2 would liquify even at -60C and even if it had a trace of water in it. Normal O2 will just barely liquify at -190C! But, as you say, if you are flying at -60, then you must be pretty high in the atmosphere and would really need that O2!

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  #18  
Old 03-29-2008, 08:27 PM
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I believe he meant DEWPOINT in the standard terminology, as in for water vapor in the gas - not the dewpoint of oxygen itself. Oxygen has a critical temperature of -118.5 C, meaning that no matter how much pressure you put on it, it won't liquify above that temperature.

The water vapor dewpoint of -60C is about right, they take atmospheric air and compress it, then chill it to about 34F to get most of the moisture to "dew" out, then chill it with an ammonia coolant loop to around -60C which causes the remaining water vapor and all the carbon dioxide to "frost" out onto the ammonia coolant loop. The remaining gas then gets routed through a molecular sieve bed to clean up anything left over and chilled further and sent to the turboexpander for liquefaction.

Sidenote to Greg - if you take a reservoir of atmospheric pressure liquid nitrogen and run oxygen through a tube immersed in the nitrogen at atmospheric or slightly higher pressure, the oxygen will readily liquify. The boiling point at 1 atmosphere for oxygen and nitrogen is only about 13 degrees C apart.
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Last edited by airguy : 03-29-2008 at 08:40 PM.
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  #19  
Old 03-29-2008, 08:42 PM
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Default Medical regulators

My medical regulator goes down to 2 lpm. Is this low enough if I use the OxySaver cannulas?
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  #20  
Old 03-29-2008, 08:58 PM
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Quote:
Originally Posted by craigvince View Post
My medical regulator goes down to 2 lpm. Is this low enough if I use the OxySaver cannulas?
I would say no. Going off the chart at http://www.wingsandwheels.com/page35.htm
it appears it uses .25 lpm at 10k feet and .48 lpm at 15k. You would be flowing between 4 and 8 times what you need.
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