Posted by Sorcerer (38.193.53.24) on July 14, 1999 at 18:58:07:
Operating a small airplane at an altitude greater than
8-10,000’ above sea level can be hazardous unless the
pilot breathes supplemental oxygen from an on board tank.
Operator/owners of general aviation aircraft face problems
similar to our own when it comes to obtaining refills for
their O2 bottles; namely, whether to pay a premium price
for "ABO," or refill the bottle at the local welding gas
supply at a fraction of that cost.
Writer, and fellow pilot John Deakin has carefully researched
the current methods of commercial production, storage and
transportation of pure oxygen and reported his findings
in an enlightening article in Avweb, the Internet’s aviation
magazine and news service. John has graciously given me
permission to refer to data from his original article.
In the interest of brevity, I have quoted "out of context."
I invite you to read his entire article at the below site:
http://www.avweb.com/articles/pelperch/pelp0013.html
"Plain air is filtered, then alternately compressed (and
thus heated) and cooled in several stages, until it is
at about 2,000 PSI and 70º F. Water is drained at each
step as it condenses out, leaving the moisture content
at near-zero.
Then the long, complex process of cooling the air begins,
with several different systems used to bring the stuff
to -275º F, and partly by dropping the pressure to about
90 PSI, where everything except the oxygen and nitrogen
is frozen, and filtered out. By playing with the temperatures,
the oxygen vapor is boiled off, captured, cooled again
to the liquid state, and stored in special double-walled
containers for transport.
Key point, here. That 90 PSI oxygen must then be re-compressed,
and this is the point that led to all the hang-ups over
"welding, medical, and aviator's" oxygen. "Medical," and
"ABO" differences of decades past. In years gone by, there
were several ways to do this. Breathing oxygen (medical
and aviator's) was compressed by water-sealed compressors
to reduce impurities added, and that nasty old welder's
oxygen might have been compressed by machinery using oil
for lubrication.
But modern industrial processes demand gases that are at
least as pure as breathing gases, so the old ways died
out, and compression is now universally done by the same
compressor, using dry lubricants and the same standards
of purity and cleanliness for all oxygen."
Bottom line: There is NO DIFFERENCE between medical,
aviation and welder’s oxygen (except the price of a
refill.) All three, "…come from the same tank of liquid
oxygen (LOX.) The liquified form is the cleanest, purist,
driest form of oxygen (or any substance) you’ll find,
anywhere."
(By permission. Copyright 1998, 1999. The Avweb Group.
All rights reserved.)