From: John De Armond
Subject: Re: Airgun CO2 Tanks
Organization: Dixie Communications Public Access.  The Mouth of the South.

Doug White <gwhite@ll.mit.edu> writes:


#The problem isn't so much with the CO2, as it is with the tanks.  If you
#start out with a dry tank, you're OK.  However, some soda vendors exchange
#tanks (like some welding outfits), rather than refilling.  This means
#every time you get a new tank, you run the risk that someone's got some
#water in it.  It you purchase your tank, and get THAT TANK refilled, you're
#probably alright.  Given that the very first person in this area with
#a match CO2 pistol that tried a soda tank got burned, no one else has
#had the nerve to try it.  If someone else wants to try using soda tanks,
#at least they will know the hazards.  I'd love to have seen you explain
#that this is a 'non-problem' to my friend as he was trying to dry out his
#brand new Walther 'water pistol'.

Perhaps I can add some facts to this since I used to own a compressed
gas wholesale company.

All types of CO2 tanks are filled from the same source.  Most CO2
comes from oil and gas wells and from refineries in La and Tx.  It is
shipped in liquid form in tanker trucks or rail cars from only
a few terminals in the country.  The liquid CO2 is typically transferred
to a refrigerated low pressure tank at the fill station, such as the one at
my company.  The actual filling involves heating the liquid CO2 to
bring the pressure up and then pumping it through a manifold to which
numerous cylinders are attached.  Welding, bulk, beverage and medical
cylinders are all filled from the same header.  It is economically
impractical to maintain multiple grades in inventory so "medical
grade" CO2 is the gas used for all uses.

CO2 quality is maintained to high standards for a couple of very
practical reason.  One is stated above.  Two is the fact that the
container costs much more than the product and the container must pass a
"visual hydro" inspection every 5 years and a true hydro every 10 years.
"Visual hydro" means taking the valve out and peering inside the tank
accompanied by a strong light.  Any visible rust or other interior
damage mandates the cylinder be deactivated and condemned.  Deactivation
usually involves drilling several holes through the cylinder.  (OB Gun
stuff: I usually used armor piercing .30-06 bullets instead of a drill.
A bit more fun :-) The primary cause of rust is moisture in the gas,
particularly with CO2 considering that it forms carbonic acid in water.
Ergo, the CO2 is maintained very dry.  I tested my bulk shipments for a
dew point of -80 deg F or better.  That's dry.

The major beverage companies have the same sort of filling station
I had.  They have added incentive to maintain quality in that
a bad tank of CO2 messes up a lot of product, makes the restaurant owner
mad and causes the company a lot of money because he will invariably
send out a new tank by company courier.  I should note in passing that
it is typical for the industrial and beverage vendors to offer
mutual aid.  I've filled beverage tanks for the local bottling company
after they had equipment problems and they've bailed me out too.

A note about cylinder ownership.  It is convention for the CO2 cylinder
to be owned by the customer.  This is in direct opposition to convention
for other pressurized gas cylinders.  Federal regulations require that
cylinder serial numbers be tracked to make sure a given cylinder's
ownership can be identified and to make sure the hydros are done
on time.  In practice this is NEVER done.  One simply takes the
empty cylinder to the gas store and is given another one - just like
the stop'n'shop propane cylinder exchanges.  The exception is
beverage cylinders which by convention are owned by the company.
The reason is the beverage biz is very competative and forcing
a restaurant owner to buy a cylinder is unheard of.  The important
point is that tanks are normally exchanged regardless of the
ownership.  I won't say that no one never fills a cylinder while u wait
because surely somewhere someone does this.  But I've never seen it.
It was simply too uneconomical to run the filling plant for one
cylinder.

If someone got a bad tank of CO2, that was a specific problem with that
tank and not anything wrong with the process.  Stuff happens.  The
biggest problem is when people drain the tank completely.  Most
contracts require 25-75 psi be left in the tank.  Beverage regulators
normally enforce this.  This is to ensure that no foreign matter can
enter the cylinder.  A cylinder that IS completely empty normally
receives special treatment which includes evacuating it before filling.

My advice would be if a beverage company will deliver you a tank
to your doorsteps at a reasonable price, then take advantage
of the convenience.  Beverage CO2 is typically significantly more
expensive because the overhead for "free delivery" is built into
the price.  Nontheless, it is a good deal since you don't have to
buy the cylinder.  One last reason is the fact that most beverage
companies have converted to aluminum tanks because they are
a bunch lighter and don't rust.

John