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>With regards to the helium purity issue: > >SNIP My supplier has a number of grades, a 6-nine Research or "Chromo" grade, a 5-nines Ultra High Purity (UHP), three or four 4-nines grades which differ mainly in how many ppms of O2 they are adulterated with and whether they have no or 1 ppm hydrocarbon. Then there's an ungraded "balloon" or low end welding grade which they only guarantee to "float a ballon". Their industrial grade is a 4 nine, and they don't seem to sell anything lower, like the 3-nine industrial grade you are getting. Anyone of them but that ballon stuff would be fine - this is very clean gas by air standards. The dirtiest grade my supplier carries has <1ppm hydrocarbons (BTW, the lab guy told me the hydrocarbon figure given for He includes all hydrocarbons, gaseous and condensed). "Ballon grade" seems to vary a lot between suppliers (and maybe batch) and is often oxymoronic, since some suppliers seem to sell an ungraded crude He, and others just whatever the lowest grade they have on hand. Obviously, if one is thinking of using balloon He for mixing the differenc could be critical. My supplier tells me their balloon He runs between 98-99% pure, but couldn't guarantee it. Prices are around $50/240cf for the industrial grades, based on 5 tanks a year. Price seems to be very flexible, with a lot of room to haggle. BTW, any supplier who has a plant where they are actually filling the tanks will have a lab there where they do the analysis and record keeping. These are the folks to call when you want answers, not the guys at the counter. I just call the companies main 800 number and ask them to give me the lab. Also, there will usually be a plant supervisor or director of ops who will know a lot. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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