[Braehill]

John,
It's been a long time since I dealt with CO2 cylinders but if I remember right the vapor pressure for
co2 is 838# @ 70* so a full cylinder will be at around 800# but it's in a liquid state at that pressure. It's a little hard to explain but it can still have that pressure even when it's almost empty. If it's down to 500#, it's probably almost empty and has not enough in it to maintain a liguid state. Not sure if that's clear enough to understand or not.

Len

[AKweldshop]

John,
It's been a long time since I dealt with CO2 cylinders but if I remember right the vapor pressure for
co2 is 838# @ 70* so a full cylinder will be at around 800# but it's in a liquid state at that pressure. It's a little hard to explain but it can still have that pressure even when it's almost empty. If it's down to 500#, it's probably almost empty and has not enough in it to maintain a liguid state. Not sure if that's clear enough to understand or not.

Len

Sort of.
I'll hook it up to a mig welder, and see if it welds.

Do you know roughly what it would cost (or should cost) to fill it???

Thanks,
~John

[Superiorwelding]

John,
It's been a long time since I dealt with CO2 cylinders but if I remember right the vapor pressure for
co2 is 838# @ 70* so a full cylinder will be at around 800# but it's in a liquid state at that pressure. It's a little hard to explain but it can still have that pressure even when it's almost empty. If it's down to 500#, it's probably almost empty and has not enough in it to maintain a liguid state. Not sure if that's clear enough to understand or not.

Len

My cylinder has a tri-mix in it not CO2, sorry.
Now that Braehill said that I remember.
-Jonathan

[Braehill]

By the picture I'm guessing that it's what they call a D1-A cylinder and they're only about 33 scf so it shouldn't cost much to fill it. It's been a very long time since I had to buy CO2. I honestly couldn't even guess. I know that I spend all day at work busting my hump trying to get rid of it while making Hydrogen. We pay for a permit to release it into the air, millions of SCF a day.

Len

[noddybrian]

That's why I commented on using small dive cylinders for decanting gas into - the CO2 cylinders don't have or need a very high test pressure as their content is held as liquid ( hence you pay for CO2 by the kg weight much like propane ) - they hold a relatively high volume of gas when it's used as a vapor due to the amount this expands from it's liquid state ( especially if you have the correct heated regulator as this is very sensitive to ambient teperature ) - but if you use the same cylinder for a compressed gas it holds very little due to the low working pressure - the lowest rated dive cylinders here will have a 232 bar working pressure & there are several sizes available in 300 bar - so you can safely decant from a new full size cylinder ( 230 bar ) without worry - or even use a air over gas intensifier pump to achieve higher pressures - this is one of the few options available to us in the UK - we can't simply walk into a shop & pick up gas cylinders ( other than propane )

[Otto Nobedder]

Braehill,

Thanks for the reminder about the triple-point properties of CO2. I've only worked on one liquid CO2 trailer, primarily installing a meter, and that triple-point thingie was a headache. The temperature TC for compensation had to be placed carefully relative to the meter turbine, and there was a minimum length of straight tube before and after that had to fit in this cabinet.

I got a little frustrated with conflicting information on the physics from the interwebs, and just installed it per spec and walked away...

Steve S

[Braehill]

After the week I've had I don't have the mental capacity to put two thoughts together let alone explain in print Triple point. But Brian has done a fine job explaining it since it seems he deals with CO2 on a useful basis, unlike me, I hate the stuff and as it gets warm outside, I hate it even more. It increases the Methane carryover which is my biggest enemy in the summer monthes. It's a waste gas in our process, altough most of the newer plants can recover it and sell it.

Len

[MinnesotaDave]

Hey John, here is a table to help explain the vapor pressure of liquid CO2 in a cylinder.

Basically, at 70 degrees and 600 psi, you should be down in the 15% full range.
It's cheap to fill so don't worry about bringing it in when you run it out.

The little white table in the upper left is a nice quick version to reference too.

[AKweldshop]

Well,
I plan on building a little bracket holder that fastens to the back of a mig welder.
I'm not sure which mig welder yet, as I am shopping for one.
I got 2 of these barb fitting dealio's, $0.25 for the 2 of them.
I'll gut that hose and made that regulator hose about 10-12in long.

Should do nicely....

~John

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