--Have listened to Ernie and am in the process of getting a flowmeter for my argon tank. The trouble is I haven't been able to find one with anything other than a 0-100cfm scale on a small column; i.e. there's insufficient resolution to see what's really going on! Anyone got a link to one that's readable?
Ernie and I went through this recently. I found some NOS Meco flowmeters on ebay that have really good resolution at the low end, essential for helium. I also like the Harris No. 355 regulator/flowmeter - it has good resolution as well. (So does the 356 dual flowmeter ..).
I cobbled up a dual-flowmeter setup using the Meco flowmeters, but then I got a factory-made dual. I'd be willing to let go of the flowmeters individually or together, whatever.
Grant Erwin Kirkland, Washington
If you're interested in corresponding about buying my flowmeters, grab my email from here:
A company named Dwyer makes lots of flowmeters for air and such. I think that you can look up the calibration constants for air and Argon and get a fudge factor to convert to Argon. Lots of surplus places have Dwyer stuff - here is one, but it is for much to low flow, 20 CFH is probably about 60x too low for welding purposes, but look around
--Well there you are; didn't even know if there were other brand names! A ThomCat search pulls in much irrelevant stuff. Here I got some good feel for what's best; now I can buy online. Anyone got a favorite web supplier?
I'd have to look it up. At one time I knew how to calculate it, but I killed those braincells... I was thinking it was based on molecular weight, but the difference between Helium and Argon isn't 7X as I remember.
Here are some sites with information on coming up with that fudge factor
Omega sells a lot of different kinds of stuff. They are good but expensive.
Ed: The proper name for the ball type flowmeters is variable area flow meters or Rotameters. Some vendors are: Brooks Instruments Cole Parmer King Vogtlin (should be an umlaut on the o but my keyboard and I don't know how)
I used to have a book with the coefficients for many gases, but it is long gone as I have not worked with that stuff for 20 years.
I found a listing in a Victor regulator data sheet that lists the correction factors, using air as 1.00, as follows:
argon 0.85 CO2 0.81 helium 2.69 nitrogen 1.02
So, if you have a flowmeter in one scale you just need to multiply by the ratio of the ratios (got that?). Example: a flowmeter for CO2 but is now using argon. If the CO2 scale shows 50 cfh, then the actual argon flow would be 50x0.85/0.81 = 50x1.05 = 52 cfh
I checked this against my multiple scale flow meter, which gives the following rough ratios: Ar to CO2: 1.03 Ar to helium: 0.325 Ar to nitrogen: 0.857
Within my eyeball measurement tolerances, this appears to be pretty good correlation to the Victor correction factors.
I think this is also reasonably close to the square root of the ratio of the gas densities (don't aks me why it should be the square root). The listed gas densities are, as follows:
argon 0.1114 lb/cubic foot CO2 0.1235 helium 0.0111 nirogen 0.0782