I have a CO2 fire extinguisher which i bought at a garage sale a few
years ago very cheaply. It is out of testing dates and will need to be
retested, I have just had it sitting in my shed and i am about to take
it in to get it re-tested so i can use it for MIG welding.
Is there likely to be any legal issues with it, could it be an ex-
rental or something? If so what markings do i need to look for to be
able to tell this as i don't know any of its history?
Any help or information would be much appreciated,
Over a few years, I've acquired 3 or 4 the same way you did, and none
of them had any signs or markings or stamped message to make me
believe there would be any problem of ownership. I've had each tested
and recharged at a reputable dealer here. Cost of doing that is well
below the cost of a new extinguisher.
Not a good idea as fire bottles are not all rated for the same
pressure levels as are
welding bottles. Working pressure for CO2 extinguishers are 2/3's or
those normally used for bulk CO2. The highest rated portable fire
bottle that I could
find was only rated for 2000psi working pressure.
The problem Wes, is how are you going to flag the cylinder to the gas
charge the bottle that it won't take the normal fill pressure? All
they look at is the
color and the valve before charging it. Do you really want to put a
bottle that is
only capable of 2000psi onto a charging line that fills bottles to
3000 or 3500 psi?
I don't know about you, but I darned sure don't want to be within a
mile of that
place when it happens. I've been around a bottle facility that went
up in flames
before. The fire department found O2 and CO2 bottles as far as 7
range. We just had a small facility go up in flames here in the DFW
area just a
couple of weeks ago. DFD found ruptured bottles as far as a mile away
one and it was tiny compared to the one that I saw as a kid in
Houston. I work
around high pressure gas systems every day and minor mistakes can kill
anyone around you in an instant. We had someone put down the incorrect
pressure when an accumulator was changed out. The resulting explosion
hurt anyone because it was contained, but it did cost well into 6
figures to repair the
damage done. This is one place where shortcuts and trying to cheap-
it, will bit you.
I don't think you understand the physics of CO2. It turns to a liquid at
moderate pressures (i.e. well under 1000 PSI, depending on the
temperature). You can try to push as much C02 into the bottle as you
want, but you can't get the pressure higher than that without getting it
really hot. It just turns to liquid and fills the tank up. It's not
like nitrogen and a lot of other gasses that don't liquify until you get
to really high pressures. You can fill a cylinder completely with
liquid, and it STILL won't be at a dangerous pressure. The only risk
would be if someone filled it completely with liquid and then sealed it,
because then it's imcompressible and a temperature rise could cause a
Anyone who is filling a CO2 cyclinder commercially will understand this,
and there shouldn't be an issue. The downside of using a fire
extinguisher tank is that it isn't designed to be banged around like a
commercial gas cylinder. They are supposed to hang on the wall & be used
in emergencies. As long as you treat them carefully, there shouldn't be
a problem if it's been hydrotested in recent memory.
Never heard of anyone having "owned" issues with fire extinguisher
AFAIK, the whole "owned" tank thing with the gas bottles is all just
part of their racket to tie you, the cutomer, to them, the supplier.
Works good, too!
You will want a hydro, and a new valve. The times I was looking at
this, they referred to the valve as a "commercial" vale. It is that same
valve used on the soda fountain bottles, with screw threads and a
shutoff valve, similar to a welding gas bottle (there's a surprise!).
If it is full, hack together some fittings to adapt it to use the gas
in it. If the outfit that is doing the hydro and refills will credit you
the CO2 that they remove, so much the better. Not a huge loss if they
don't, just goes against my cheap nature to waste the stuff.
CO2 pressures are low, on the order of 800 psi, without overheating
the tank or overfilling it, and your biggest risk is that the seals are
shot to heck on the valve itself, and it leaks once opened and under
pressure, in which case, you are no further behind. Fire valves may not
be pressure tight, downstream of the poppet valve, or around it's stem
(the part of the valve pushed in by the handle on the extinguisher), as
their intended use is to dump the product on demand, if that makes sense
CO2 bottles are filled by weight, not pressure.
Similar to BBQ propane, the CO2 is a liguid under a layer of gas in
And it's not like acetylene, where filling the bottle too fast or to
too high a pressure will make things go ugly.
Let the guys at the depot decide if the bottle is a disposable or if
If it is not of the disposable variety, they will be quite OK with
hydro and fill.
CO2 fire extinguishers (FE) are not normally rented, they are sold.
If you don't see "PROPERTY OF FOOTROT FLATS SCHOOL DISTRICT" stamped
on the neck you are probably clear. The service people aren't going
to run the serial number with the police unless you give them cause to
be suspicious, they just fill them.
To get the best price and turnaround time, make sure you find the FE
service company in your area that actually has the hydrotest cell and
the filling gear on site - otherwise they send the work out to the
people who do, and mark up the price to make some money on it.
There has to be an identification and instructions band, and it has
to be readable. There has to be a readable serial number on the band,
so they can log the recert.
The cylinder can't be all dented up or rusty - if the paint isn't
perfect sand it down and give it a fresh coat BEFORE it gets bad. You
will have to touch it up where they stamp the new hydrotest date.
And it has to be made by an FE company that is still in business or
where they can get 'certified repair parts' from a successor company -
it's silly, but for liability reasons they can't buy and use 5c bulk
O-rings from McMaster, they have to buy the part through the FE maker
for a buck each for the liability insurance.
(YOU can find and install an exact equivalent replacement part, as
long as you don't tell the FE service guys you did it... But you have
to be certain you have the exact size and materials, or it can fail in
use. And the whole thing about a FE is that it can sit for years but
has to work when you need it to, so don't take any shortcuts.)
If the manufacturer is long gone and the FE parts are no longer
serviceable, you can get a new CGA valve and have them hydrotest and
convert the bottle for welding or beverage CO2 use.
But if it's still usable as an FE it's more valuable as one - get
yours filled as a FE and ask the service shop for a welding gas
cylinder. People throw the whole FE in the trash if the valve or horn
is bad, or the label/band is unreadable and they can't be used as a FE
anymore. All you pay for is the valve, hydrotest and fill.
Doug: I do remember most of the physics of pure CO2, but in this case
I'll plead brain fart
partially due to way too many days with nearly no sleep over the last
couple of weeks. It's
also been nearly 15 years since I worked with CO2 by itself. Normally
I deal with N2 and O2
and mixtures of various gases at pressures well above 2000 psi as well
as LN2 and LOX.
What I remembered, and missed was the absolute pressures on the vapor
pressure curve given the
bottle fill percentage vs. ambient temp. What I was remembering
correctly is that the
bottle pressure will rise approximately 500 psi for a jump in bottle
80F and 90F, when the bottle is over 60% full and less than about 90%
full. I simply
displaced the curve about 50% upward.
BTW: There are now some commercial processes that are using CO2 in
liquid form at
pressures in the 1500-2000psi range.
I think the intension - I hope - is to use it as fire prevention.
Normally they are to small for MIG except for tiny pony and portables.
The largest I have seen was mounted on two 4' tall metal wheels.
But the largest tank CARDOX was outside a paint house at a GM plant.
Fire suppress the entire building in seconds.
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
Lots of good advice from others but I did not notice anyone letting you know
that fire extinguisher bottles have a dip tube to draw liquid from the
bottom of the bottle when being discharged. For welding you will want to
draw gas from the top. This should not be a problem if the valve is
replaced, as the dip tube is connected to the valve. Just for your