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Can I tell how much Co2 Argon is left by weight?

Discussion in 'The Hokey Ass Message Board' started by Mutt's37Buick, Jan 8, 2013.

  1. Mutt's37Buick
    Joined: Mar 28, 2011
    Posts: 174

    Mutt's37Buick
    Member

    I bought a used MIG welder over the weekend with a partially used CO2/Argon bottle.
    The bottle is 3 ft tall, labeled AirGas and I believe is their 80 Cubic ft size. The bottle weighs 50 lbs.
    1) Is there any way to determine how much gas is left in the bottle from the weight?
    Thanks
     
  2. mink
    Joined: Oct 4, 2007
    Posts: 1,321

    mink
    Member
    from CT

    How about hooking up your regulator with its pressure gauges. Compare your tank pressure to....
    my tanks not full...maybe someone else has a value
     
    Last edited: Jan 8, 2013
  3. pressure tells the story think 1500 is about full could be higher
     
  4. LongT
    Joined: May 11, 2005
    Posts: 966

    LongT
    Member

    The weight of the Argon is probably insignificant, Airgas website stated 49 pounds full. Pressure isn't REAL accurate either as the pressure will vary with the temperature. You'll get a ballpark though with the pressure which is about all you need.

    Found a dealer, not Airgas,but probably VERY similar - Full Pressure: 2200 PSI @ 70 Degree F


    Bill
     
    Last edited: Jan 8, 2013

  5. truck
    Joined: Feb 24, 2009
    Posts: 116

    truck
    Member
    from Brisbane

    Try pouring hot water down side of cyl, not sure if works with argon blends but many gases will show you an pretty exact line of condensation on side
     
  6. Mutt's37Buick
    Joined: Mar 28, 2011
    Posts: 174

    Mutt's37Buick
    Member

    I've used water that method for propane bottles. I'll give it a try on this bottle.
    Thanks everyone for your help.
     
  7. Wow, this is actually something we learned in college welding class, and here it is coming back to be useful. Yes, you can determine by weight. First you need to consider your mixture, 75/25 or whatever it may be. Then you need to get the weights for each gas...
    Argon: 1 cu ft= 0.103 pounds
    CO2: 1 cu ft = 0.114 pounds
    Now just a glance at those numbers, and the realization that we're talking 80 cubic feet shows that the differences aren't going to be negligible. Since these two gasses are so close in weight, and for quicker work you can just average the weight of the two, and then multiply or divide to get your desired results. If you were looking for highly accurate results, or if the gas weight values were more varied, you would need to consider the percentages, and adjust accordingly.


    OR, you could cheat, and find a scale like this where someone has already done the work for you. There's roughly, 8.5 pounds difference between an empty bottle and a full one. My quick math done by averaging the two weights showed 8.68 pounds. That shows the necessity of considering percentages for more exact work.

    http://www.havardwelding.com/welding_gases_argon.htm

    We did this expiriment with a full "K" size oxygen bottle. Most people said things like what has been said here. Yes, the gasses aren't that much different in weight from atmosphere, but, when you consider how much is jammed in there, the weight really adds up.
     
    Last edited: Jan 9, 2013
  8. Mutt's37Buick
    Joined: Mar 28, 2011
    Posts: 174

    Mutt's37Buick
    Member

    Thanks very much.
    That chart is exactly what I'm looking for.
    On a differet website I was told the empty weight will be stamped on the bottle. Have not looked for it yet.
    With this info I could calculate exactly what I have.
    I remember I had a BarbeQue once that used a spring lever arrangement that held the bottle. A pointer & scale showed when the bottle was getting low.
    Could probably set up something similar on my welding cart.
     
  9. mink
    Joined: Oct 4, 2007
    Posts: 1,321

    mink
    Member
    from CT


    That would be a waste of time. More practical to open eyes and look at pressure gauge
     
  10. dreracecar
    Joined: Aug 27, 2009
    Posts: 3,281

    dreracecar
    Member
    from so-cal

    Get another bottle and fill it up. When the first one goes empty switch and get the first one filled again. Knowing that there might not be enough gas make you exchange a "Not empty" bottle for a full one?
     
  11. indyjps
    Joined: Feb 21, 2007
    Posts: 4,893

    indyjps
    Member

    if the bottle is stamped with Airgas name, you have to take it to an airgas dealer. other companies wont accept a stamped bottle from another company 9im sure there are exceptions)
    when you get a new bottle, be sure to get one with a "blank collar", no company name stamped on it.
     
  12. I've never been that concerned about running out, but, I suppose if you were you could just get a bathroom scale, and make it part of your welding cart. Put it under the bottle, and incorporate it in your design. There's no shortage of second hand bathroom scales around either. Weigh the bottle full with the regulator on, and then mark the bathroom scale to read when it's running low.

    As for relying on the pressure gauge, I haven't seen a high quality gauge to read tank pressure on any regulators in quite awhile. It seems most of them are pretty flakey. Usually the regulator gauge is good, but, the tank pressure gauge isn't real great. Especially the ones that come with a super 110v machine. Also, as has been said, pressure changes according to temperature, and other conditions. Anyone here ever had a bottle that was "out" last them another month and a half of use? I know I have.
     
  13. bald_and_grumpy
    Joined: Mar 13, 2010
    Posts: 122

    bald_and_grumpy
    Member

    At 2200 psi, your cylinder will have about 10.8 pounds of product in it. If the tare (or empty) weight of the cylinder is stamped on it, then you can subtract the tare weight of the cylinder from the actual weight of the cylinder, and that will tell you how much is left. Tare weights are measured without the cylinder cap or regulator on the cylinder. Not all cylinders will have a tare weight stamped on them. If it doesn't, then pressure will be a pretty good indicator of what's left in the cylinder.
     
  14. '51 Norm
    Joined: Dec 6, 2010
    Posts: 760

    '51 Norm
    Member
    from colorado

    OK welder guys, I have a question that has been wandering around in my head for some time.

    CO2 liquefies at around 150 PSI. Argon dosn't. When the gas is mixed (25/75 or whatever) Does the CO2 still liquefy at pressure leaving the Argon behind? If so it seems to me that the argon would get used up first and then the CO2. I can't see how that would work very well.

    Where I work we have CO2 bottles for the fire protection system and we have to weigh them occasionally to see if they are still full. We have been experimenting with a system to measure the temperature difference on the side of the bottles to detect the liquid line. A full 80 cubic ft bottle has 100 pounds (+ or -) of liquid CO2 in it.
     
  15. bald_and_grumpy
    Joined: Mar 13, 2010
    Posts: 122

    bald_and_grumpy
    Member

    At pressures under 2000 psi, the co2 won't liquefy when it is only 25% of the blend. You can think of it sort of like the argon is holding it up. Once the concentration of co2 rises above about 30% of the mix, then the top pressure of the mix starts to decrease because the co2 will start to condense.
     
  16. bald_and_grumpy
    Joined: Mar 13, 2010
    Posts: 122

    bald_and_grumpy
    Member

    And before the science police flame me, I know that the argon isn't actually holding up the co2. I know that the co2 is holding itself up in accordance to the law of partial pressures.
     
  17. On our bottles here at work and my ones at home, I just watch the cylinder side of the regulator - mine all seem to be very accurate.
    You kind of learn how long a bottle will last based on the pressure reading. At home where I am not doing a lot of constant welding I let it run to Zero and then go exchange it. At work when we see it down to about 200 lbs we make sure there are replacements int he rack
     
    Last edited: Jan 9, 2013
  18. '51 Norm
    Joined: Dec 6, 2010
    Posts: 760

    '51 Norm
    Member
    from colorado

    Thanks bald & grumpy. I have wondered about that for a long time. I suppose that it is something like lowering the freezing point of water by diluting it with glycol.
     
  19. I'm thinking CO2 doesn't always liquefy under pressure. I'm no chemist, but you can get the same size bottle filled with straight CO2 for MIG welding (lower cost). It's still vapor at 2000psi, and the bottles don't weigh any more than a bottle of 75/25... ????
     
  20. CutawayAl
    Joined: Aug 3, 2009
    Posts: 2,144

    CutawayAl
    Member
    from MI

    I believe the tanks are filled by weight rather than pressure.
     
  21. bald_and_grumpy
    Joined: Mar 13, 2010
    Posts: 122

    bald_and_grumpy
    Member

    Exwestracer, pure CO2 will not be at 2000 psi at a reasonable temperature (less than 400 or 500 degrees or so). The highest pressure I have ever seen pure CO2 at is about 1100 psi, and that was in a black cylinder in the hot Texas sun. Usually, pure CO2 has a vapor pressure of around 660 psi.

    CutawayAl, those kind of mixes can be filled by weight or pressure. The welding style mixes are usually done by pressure because it's easier to fill a bunch of cylinders at once that way. If you are working with a smaller number of cylinders, the filling by weight is much more accurate.

    I don't mean to be a know-it-all, but I have a degree in atmospheric science, and I am a cylinder gas blender for Airgas. I have been doing this for about 20 years.
     

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