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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'.
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