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Originally Posted by DDC_Dan

Here's a reference for purity levels for various grades of CO2 (from the same company hvac5646 used).
It lists welding/industrial grade CO2 as 99.8% pure, and less than 32ppm H2O.
To be clear, the reference was only for Nitro. This is not the same company reference the Boss uses to buy our dry co2.
http://www.abbottwelding.com/index.p...urity%20Levels

CO2 is NOT an inert gas as some have stated. At least at steel welding temperatures it is known to react with the weld puddle, causing embrittlement. Not saying that it would be inappropriate as a braze-purge though.
Gafadlefarb! Co2
is the end of the combustion process. It cannot not be broken down further unless improbably high pressure and temperature are applied to it; coCOnditions you would never see in naturally occurring events. That is the definition of an inert gas,

I would like to see a comparison of brazed joints (cut open) using N2, CO2, and no purge gas (not open tubing like I have seen on YouTube, but with ends nearly sealed, just enough to allow pressure to escape but not allowing free flow of air). I am not aware of any published tests thus.

CO2 not being an inert gas is the biggest mis- conception that comes up when the topic of using dry CO2 is raised

Here's a reference for purity levels for various grades of CO2 (from the same company hvac5646 used). It lists welding/industrial grade CO2 as 99.8% pure, and less than 32ppm H2O.

http://www.abbottwelding.com/index.p...urity%20Levels

CO2 is NOT an inert gas as some have stated. At least at steel welding temperatures it is known to react with the weld puddle, causing embrittlement. Not saying that it would be inappropriate as a braze-purge though.

I would like to see a comparison of brazed joints (cut open) using N2, CO2, and no purge gas (not open tubing like I have seen on YouTube, but with ends nearly sealed, just enough to allow pressure to escape but not allowing free flow of air). I am not aware of any published tests thus.

Originally Posted by hvac5646

See what i mean about confusing?
Did he say as a braze purge or just to blow out drains?

Around here food grade CO2 is soda fountain CO2.

Industrial MIGHT come under the category of shield gas for welding and that is what we use.

It is a Cat III rating.


The Bone Dry is 9 PPB according to the chart you posted. I don't think nitro even comes anywhere near that.

airgas guy specifically stated his customers had been buying industrial grade Co2 for pressure testing HVAC systems. unless one is pulling a deep vacuum before pressure testing odds are there will be traces of moisture inside system anyways. Co2 has been used as a shielding gas for welding for decades.

we are way over thinking this

costs for a 50lb cylinder exchanged, industrial Co2 is about $50 ... vs 3x-4x higher costs for bone dry Co2 ..

Want even more confusion? http://www.abbottwelding.com/index.p...urity%20Levels

Originally Posted by cy

here's airgas Co2 technical description link to pdf ... bone dry is listed as 99.9%
http://www.airgassgcatalog.com/catalog/pg013.pdf

Linde food grade Co2 is listed as 99.9%
http://www.google.com/url?sa=t&rct=j...45645796,d.b2I

someone correct me if I'm wrong ... from what I've been told by Airgas folks ... most times difference between grades of Co2 is amount of time/effort to analysis gas for purity. have been told by different sources that industrial grade Co2 is identical to food grade Co2. differences are how container is lined.

back to what the old timer at Airgas told me ... just use the industrial grade Co2 and quit worrying about it.

See what i mean about confusing?
Did he say as a braze purge or just to blow out drains?

Around here food grade CO2 is soda fountain CO2.

Industrial MIGHT come under the category of shield gas for welding and that is what we use.

It is a Cat III rating.


The Bone Dry is 9 PPB according to the chart you posted. I don't think nitro even comes anywhere near that.

here's airgas Co2 technical description link to pdf ... bone dry is listed as 99.9%
http://www.airgassgcatalog.com/catalog/pg013.pdf

Linde food grade Co2 is listed as 99.9%
http://www.google.com/url?sa=t&rct=j...45645796,d.b2I

someone correct me if I'm wrong ... from what I've been told by Airgas folks ... most times difference between grades of Co2 is amount of time/effort to analysis gas for purity. have been told by different sources that industrial grade Co2 is identical to food grade Co2. differences are how container is lined.

back to what the old timer at Airgas told me ... just use the industrial grade Co2 and quit worrying about it.

When the Boss first started searching for a CO2 supplier he talked to Air gas. He found there was no consensus from the staff on what Bone Dry really is.

So now we order by purity...98.9995 to 99.99995.

But it always comes up the right part number on the invoice.

I called them to day and the guy was clueless til I told him I wanted a Cat III to IV CO2 purity. He said it "was not in the system" and would call back wit a price.


Still waiting.

Like I said...its confusing. Boss knew what questions to ask to get us the right grade.

Originally Posted by hvac5646

Then you got the wrong guy or something else is wrong. WE buy by part number off Air Gas sit for the 57 lb tank.

And it ain't high cost at all.

what grade are you buying? Bone dry or plain ole industrial grade?
Airgas guy is saying the industrial grade works just fine.

Originally Posted by cy

finally got a straight answer from an old timer at Airgas. he'd been selling Co2 industrial grade to folks for HVAC work for 30+ years. he said Bone dry grade would raise cost so high to be not worth it.

Then you got the wrong guy or something else is wrong. WE buy by part number off Air Gas sit for the 57 lb tank.

And it ain't high cost at all.

finally got a straight answer from an old timer at Airgas. he'd been selling Co2 industrial grade to folks for HVAC work for 30+ years. he said Bone dry grade would raise cost so high to be not worth it.

Originally Posted by cy

welding shield gas is industrial grade, which is same as food grade according to folks that I've talking to.

already googled up a storm on CO2 purity ... found all sorts of info, but needed to find out what everyone else is using.

Sorry, i see what you mean. We buy our dry co2 at Proxair and Air gas. The purity is 99% to 98%.

If you get that purity than you will be good.

It's confusing, I know.

Originally Posted by hvac5646

Grade III CO2 is all you need. It is a welding shield gas.

Google CO2 purity.

welding shield gas is industrial grade, which is same as food grade according to folks that I've talking to.

already googled up a storm on CO2 purity ... found all sorts of info, but needed to find out what everyone else is using.

Originally Posted by cy

thanks .. what grade Co2 is everyone using ... bone dry grade is hard to find around here and more expensive than nitrogen. can't seem to get a straight answer from local gas supplier as to purity of food grade, industrial and medical grade purity?

Grade III CO2 is all you need. It is a welding shield gas.

Google CO2 purity.

Originally Posted by hvac5646

And on the six ponder the best you can get is about 3.25 lbs refilling from a larger tank... and that was pulling the MBK 6 into a vacuum .

thanks .. what grade Co2 is everyone using ... bone dry grade is hard to find around here and more expensive than nitrogen. can't seem to get a straight answer from local gas supplier as to purity of food grade, industrial and medical grade purity?

Originally Posted by mark beiser

While I agree on principle, my experience in over a decade of refilling the smaller 1.25# RBK-6 mini tank, from a 20# cylinder I keep on my truck, is that the chances of over filling the tank are pretty much zero, unless you stick the smaller tank in the freezer for a couple of hours first.

And on the six ponder the best you can get is about 3.25 lbs refilling from a larger tank... and that was pulling the MBK 6 into a vacuum .

I can tell you the boss is POed over his MBK 6,

The dnag thing leaks...at least the one he has. He had filled it over the fall and put it in the front seat of his truck and to day he checked it and it was empty. The 25 lb tanks we filled last year off the big tank are still full.

We are going to aluminum tanks to replace the MBK 6s,

Originally Posted by cy

don't agree with how to fill instruction ... IMHO refilling needs a flex hose with target tank sitting on top of scales. to make sure weight does not exceed safe limits. CO2 tanks expand when heated. how much liquid CO2 inside tank determines safety at high temps.

While I agree on principle, my experience in over a decade of refilling the smaller 1.25# RBK-6 mini tank, from a 20# cylinder I keep on my truck, is that the chances of over filling the tank are pretty much zero, unless you stick the smaller tank in the freezer for a couple of hours first.

hmmmm .. dry CO2 may be OK to pressure test with?
been using CO2 as shielding gas for welding steel for years.

just scored one of these ... sure is a pita/$$ refilling small nitrogen tanks and getting not much capacity to boot.
this tiny tank with CO2 has a 22cu ft capacity on top of being able to fill from a larger tank. making usage down right cheap.

been filling Co2 tanks for years with paintball and airguns. don't agree with how to fill instruction ... IMHO refilling needs a flex hose with target tank sitting on top of scales. to make sure weight does not exceed safe limits. CO2 tanks expand when heated. how much liquid CO2 inside tank determines safety at high temps.

Originally Posted by ckartson

OK I picked up, that you were irked by my post. Since this thread I have been reading others and talking to other people and see that it is possible to use co2 in the state you are using it in. I have heard of people using co2 through my 32 yrs and thought they were using soda fountain stuff. Now as far as availability, our supply houses have an abundance of nitrogen and soda fountain co2 for clearing drains and blowing out coils etc. I will investigate availability of dry liquid co2. Also if a system is purged and leak tested with dry co2 and there were warranty issues (hypothetically speaking) you may have to prove you case for dry co2 as you are here because most IOM say to use dry nitrogen.

No warranty issues. Ask any comp mfgr about dry co2 they will endorse it.

Used to be common as Nitro is today.

OK I picked up, that you were irked by my post. Since this thread I have been reading others and talking to other people and see that it is possible to use co2 in the state you are using it in. I have heard of people using co2 through my 32 yrs and thought they were using soda fountain stuff. Now as far as availability, our supply houses have an abundance of nitrogen and soda fountain co2 for clearing drains and blowing out coils etc. I will investigate availability of dry liquid co2. Also if a system is purged and leak tested with dry co2 and there were warranty issues (hypothetically speaking) you may have to prove you case for dry co2 as you are here because most IOM say to use dry nitrogen.