Hi Tod,

Actually I know of some tests done by NS Research, the company that makes
automated nitrox blending stations.
They used sensors inside the tank to find out what the temperature does.
Seems that the temperature rises in a step function, meaning that the
initial flow is of big importance and after that it kind of stabilizes
(rises very slowly over the rest of the fill). After the fill it slowly
comes back to the ambient temperature.
I am not saying you can start slowly and then crank up the flow without
being punished with hot fills but if you use a more precise valve, like a
Whitey metering valve that controls the flow you can start a slow initial
flow and then crank it up a little. Typically a fill will take 5min in order
to keep it reasonably cool this way without any water.
The heat transfer over the cylinder walls does not really tell you precisely
what the gas temperature is inside the tank. Using a water filled bucket of
some sort only works when you leave the tank inside the water for a longer
period. What most diveshops do however, is fill the tank and take them out
of the water and fill the next. That will not work effectively at all.

Best Regards,

THOMAS


> -----Original Message-----
> From: Todd Baldi [mailto:todd_baldi@ho*.co*]
> Sent: Friday, October 20, 2000 10:20 AM
> To: trey@ne*.co*; Bakalite@ba*.co*; techdiver@aquanaut.com
> Subject: RE: Pony's and deep air
>
>
> Trey,
>
> Interesting post here. I had a question regarding heat expansion. I have
> heard a lot of differing opinions on methods to reduce heat
> expansion during
> filling over the years.  A shop near where I taught spent a ton
> of cash on a
> refridgeration system and advertised "ice cold" fills.  When I
> filled tanks
> I would put a 200 psi overfill, let it sit for 5 minutes, put a 200 psi
> overfill in again, and I could usually hit the target pressure on the
> button. This was with the tanks in a water bath but not refridgerated.
>
> I was told a Professional Scuba Inspector trainer and a DOT Hydrostatic
> instructor that the water doesn't do anything other than make you
> feel like
> it gets the tanks cooler quicker. They also recomended I tank 30
> minutes in
> filling a tank to the required pressure to let the heat dissapate.
>
> My thought, after filling thousands of tanks over 12+ years, is that the
> water does help dissapate some heat but the temperature of the
> water isn't
> consequential whatsoever.  It also provides peace of mind and
> helps you see
> any leaks in the tank valves. Have you ever seen any studies on
> dry vs wet
> tank filling. Is it all bullshit or is there some creedence to having the
> water there?
>
> Thanks,
>
> TB
>
>
> >From: trey@ne*.co* (Trey)
> >To: "Paul Braunbehrens" <Bakalite@ba*.co*>, <techdiver@aquanaut.com>
> >Subject: RE: Pony's and deep air
> >Date: Wed, 18 Oct 2000 14:37:31 -0400
> >
> >Paul, to carry a bottle as a stage according to all out stage
> protocol and
> >bottle marking rules is fine, but implies doing a dive  for which you are
> >not geared correctly in the first place. True redundancy means a dual
> >outlet
> >manifold with hoses configured DIR.
> >
> >To have a bottle strapped to your tanks is bullshit - none of the correct
> >protocol can be applied. To have a pony and doubles is farm animal.
> >
> >Air is bullshit at any depth.
> >
> >Below is my gas mixing and bottle marking / deployment protocol.
> >
> >GAS MIXING LESS THE BS:
> >
> >  Let's assume all bottles are correctly marked - that means MOD only,
> >horizontally, in three inch high letters , on either side of the upper
> >bottle in the orientation of the tank. All tanks turned off, all regs
> >parked. To deploy, we locate the bottle by MOD, we remove the
> reg and put
> >it
> >in our mouth, we then relocate the bottle by MOD, and turn if
> on. If we can
> >breathe, we are breathing the right gas.
> >
> >Now, mixing. First put two pieces of tape or one GUE split tape on the
> >empty
> >bottle. Hook up to either gas, but I do helium first since I
> want my oxygen
> >addition to be more in the middle of the operating range of the
> gauge, but
> >it can be done either way. Figure the correct amount of helium
> for your mix
> >considering coefficient of expansion and heat expansion. Helium will need
> >about 17% overfill to get the % you seek. Let's say we want 50%
> and we are
> >filling to 3000. Fill the tank first to 1750 to get to half, but then add
> >another 10% or so for heat expansion, so go to a total of 1900
> roughly. It
> >should cool back to 1750 or so. No sense getting real anal here, the heat
> >expansion is simply equal to the ratio of absolute temperature change,
> >using
> >the Kelvin scale - just guess at it. Turn the bottle off, but do
> not remove
> >the whip until you have written down the contents of the tank
> and the date.
> >Now remove the whip .
> >
> >Now, add the oxygen. Keep in mind that it will be heated and
> expanded, but
> >not too badly. Go a little over your intended amount but not too much.
> >Calculate this independently of the helium, and add it without regard for
> >the "pressure" of the helium. If you added the oxygen fist, keep in mind
> >that it will have expanded as well from the heat of the helium
> filling and
> >be giving you a higher overall helium pressure reading than you really
> >have,
> >so add a touch there if that is the case over and above the other two
> >reasons. Do not remove the whip until you have written down  the new gas
> >added and the date. Analyze it if you please, to solve for the
> helium later
> >to satisfy yourself.
> >
> >Now add the air, unless that was heliox and we are done. Immediately
> >analyze
> >the gas and write the analysis on the other piece of tape or the split
> >tape,
> >write the date on it as well,  and take the original tape off
> the tank and
> >cover the valve with it to indicate that the tank is full. Do
> not move the
> >tank until this is done. Obviously , the analysis should jive
> with the MOD.
> >To dive the tank, you can remove the tape so as not to litter ( and
> >obviously the only thing we go by in water by is MOD ) , but if
> you do not
> >use the tank, retape it and the valve, rewrite the contents and date, and
> >transport that way, including partially full tanks that you
> intend to reuse
> >( I reuse my deco tanks for two dives usually, so I may write something
> >like
> >"2000 psi 50%  10-18-00") . If you use it and are not going to
> reuse it,
> >it
> >is now assumed that the tank has some amount of that gas in it,
> but can not
> >be used again unless reanalyzed, so is not retagged. It can not be stored
> >full without a tape, and it can not be transported full without a tape.
> >Doubles can not be stored untagged if they have gas in them, and if that
> >mistake is made, dump the partial gas and remix rather than adding to a
> >mix.
> >A lot of people fool themselves this way on the helium %.
> >
> >Now , sorry about the car post to Kane, but he is such a Granny.
> He drives
> >a
> >Jaguar, if you can believe that one. I like the most rocket I
> can get, and
> >they just came up with a new one that is beyond ridiculous, so I
> got one.
> >So
> >what.
> >-----Original Message-----
> >From: Paul Braunbehrens [mailto:Bakalite@ba*.co*]
> >Sent: Tuesday, October 17, 2000 12:30 AM
> >To: techdiver@aquanaut.com
> >Subject: Pony's and deep air
> >
> >
> >The subject of ponies and deep air has recently come up on Scuba-L as
> >some of you may have noticed.  Some of the people have asked for
> >clarification of the DIR view on this, and I've tried my best, but
> >being the stroke I am I failed miserably.
> >
> >So, if someone here would be so kind as to give me a concise and if
> >possible reasonably polite rundown on the DIR position on Pony
> >bottles and on deep air, I would appreciate it.  I already know that
> >DIR is against the use of ponies, so you can leave that part out.
> >Exact reasons why would be welcome.  As far as deep air goes, what
> >constitutes "deep", and some references to actual fatalities brought
> >on by deep air (and I'm not talking 400 feet here, but people who
> >kicked the bucket doing what a rec. diver might do on a deep air
> >dive).
> >
> >I know this stuff is in the archives, but I'm hoping someone has
> >something like a baker's dozen handy for these two topics.
> >
> >Thanks.
> >--
> >Paul B.
> >--
> >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'.
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>
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