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Jim, Since I fill the cylinders slowly there is not much heating going on. I suppose you could test this by doing a fast fill (with the O2) and let us know. If we don't here from you we will pretty much know what happened (wink). If temperature were an issue then warming a tank after there is a known good mix should throw off the measurement. I always measure my mixes in my garage (my safe haven) so it is a bit on the cold side. I do not wait until I am on the boat to check the mix (that comes under the heading of preparation). Comments. Regards Steve -----Original Message----- From: Jim Cobb [mailto:cobber@ci*.co*] Sent: Thursday, April 08, 1999 4:55 PM To: Steve Hogan; pdisler@io*.ne*; silent@cu*.ne* Cc: Tech Diver Subject: RE: Trimix Question I don't know about you guys but I think the problem we are dealing with here is the temperature of the mix rather than stratification. As the mix cools off the reading becomes more accurate. Jim Sender: Steve Hogan Date: 4/8/99 6:53 PM > >I have run into this and have modified my mixing procedures >so that after I add the O2 to the helium I wait 1 day (I >usually mix at night so waiting around is not appealing) >before measuring the O2 % (O2 & He). It is not hard to figure >out what percentage I expect after mixing O2 with He. >Next step is to add air, wait a few hours (usually doing >something else) and then measure again. >I fill about 50 psi/min so I expect to not get much mixing from >Brownian motion. > >Steve > >-----Original Message----- >From: Patricia Disler [mailto:pdisler@io*.ne*] >Sent: Friday, April 09, 1999 1:14 PM >To: S I L E N T I M M E R S I O N >Cc: techdiver@aquanaut.com >Subject: Re: Trimix Question > > > > > >At 09:16 AM 4/8/99 -0700, you wrote: >>Frank, >> >>>Not me, but I do let the filled tanks rest a day before analyzing. An if >>>you want to tell me >>>thats not neseccary I recommend that you try this: Fill oxygen, top with >>>air, wait a minute, >>>analyze mix, turn the tank so that the valve faces ground, wait another >>>minute and than >>>re-analyze the mix. >> >>And it's the same... or not? >>When filling a tank the temperature and pressure are high which in turn >>gives a high diffusion coefficient. Makes the mix homogeneous almost >>instantaneoulsy (couple of seconds). >>What kind of differences do you get? >>What kind of analyser do you use, are you sure the hoses are drained when >>using a regulator or something? >> >>Regards,> >>THOMAS > >I have witnessed Nitrox mixtures take a while to fully homogenize. Several >years ago while mixing 80/20, (Yeah I know don't start) it came out 63% O2 >approx 30 min after the very s-l-o-w top off to fill pressure. Yes I >checked the calibration of the aynalizer (Teledyne TD-50). Each time I >would check the O2 reading would climb. I did this over a period of several >hours. Later it was right on 80%. >I'd have to say stratification can and does occur, esp. if there is not >enough turbulence during top off. >I have never seen this with Trimix as the fill rates are much higher. >However I suppose it could occur if they too were topped slowly. >At any rate I never seem to dive my gas until they show the correct mixture. > > > >"SILT HAPPENS"JD JEFF DISLER > SAFE CAVING NSS 26000 >-- >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'. > ------------------------------------------------------------------- Learn About Trimix at http://www.cisatlantic.com/trimix/trimix.html -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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