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Mr. Will, your idea for the small filling is a good one. Otherwise, you would need a very good guage, an accurate temp to figure the expansion on the fly, and a fast hand. Good solution. - G William M. Smithers wrote: > > George, > > These are really good points, especially seeing as I usually > end up doing my gas-mixing at 11PM after a couple of beers. :) > A formal gas-mixing checklist is a great idea - its > way too easy to get cavalier with a fill whip. > > The problem with guaging low-o2 mixes is especially problematic > with a CCR, since you are typically filling a dinky bottle. After > a bit of experimentation, I found mixing in small bottles to be > virtually impossible. So what I started doing is mixing up > the Heliox or mix in a set of double 104's, then trans-filling to > the smaller cylinders (6,12,or 30 cu ft). At least that gives > a greater margin of error. And 240 cubes of mix will last > damn-near forever on a CCR. I mixed up a doubles-full of 10/90, and > another of 13/44, and I expect I'll make it half way > through next season without refilling (besides, I had to have > *something* to do with those now-useless doubles). That, and > a couple of AL80's of the same mixes for OC bailout (which I will > probably never need to use), and I'm set - travel diving aside, > of course. > > -Will > > On Fri, 14 Nov 1997, G. Irvine wrote: > > > Will, this 2 percent problem is not too bad when you are partial > > pressure mixing for middle readings, like 35%, for example.You have the > > double check of the partial pressure and the reading, and the use of the > > gas is not a problem from either a toxicity or a decompression > > standpoint. Where this gets tougher is maxing the real deep mixes, but > > then the partial pressure still applies and the totals are still valid. > > You can start to see where the rebreather becomes a problem, however. > > > > The big trick is to be sure you actually added the gases in mixing ,and > > did not have a valve off while you THOUGHT you added 35 psi of oxygen, > > or some such number, when in fact you did not, and then the miniox > > reading seems "acceptable". > > > > A real good anal way of doing this proceedure is what is necessary to > > get it right. Bill Mee and I do it together, and we have a whole > > checklist to go through before disconnecting the tanks, and in the whole > > process. > > > > Adding oxygen to a high helium mix can feel like yoiu are adding it when > > youi are not. Just presurizing a big fill line fr9omt hat pressure to a > > small increment higher, even with a very accurate digital guage is a > > fooler since you can hear the gas moving even when the tank is not in > > fact open to accept it - a real dangerous situation. You have to > > depressurise the line afterwards and note the tank change on the same > > guage that the system was on to begin with , and you must do it quickly. > > There is no way the pressure has risen without the addition, even if the > > number is thrown off by the cooling - it can not decrease. > > > > Little double checks like that , and then immediately throwing the > > analyzer on the result will give you some comfort. The go and throw it > > ont he pure helium to be sure it is not offset. A lot of work, but you > > are always betting your life with this stuff. > > William M. Smithers wrote: > > > > > > On Thu, 13 Nov 1997, Jim Cobb wrote: > > > > > > > Julian- > > > > If you are worried about it, throw in a 5% safety factor instead of a 2% > > > > saftey factor, which is what we do when mixing in adverse conditions. > > > > > > You know, how many of you guys have actually read your MiniOx I manual? > > > +-2% is what the sensor is good for. That's 4% total, which > > > is either pretty scary, or pretty indicative of the default conservatism > > > that's built into modern tables and deco algorithms. > > > > > > The fact that it also quotes such potential "skew" factors > > > as 0.000X% for a Helium component is *such* a joke, in light > > > of the overall precision. > > > > > > -Will > > > > > > -- > > > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > > > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > > -- > > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > > > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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