Dry Fill?

[ScubaKris]

I dive the local springs a few miles from my property in Florida often, Morrison, Vortex, Cypress. I see people getting upset when their fill is onlly 2999 when it should be 3000. The new guys normally get stuck on tank fills for the day at Vortex and won't fill one over 3000. Heck, when I come back and put a tank on the compressor, when I check it, anything over 2500 I pull it and put on another,. I still often surface with 800psi. If your air margin is that tight, ..get a bigger tank.

 

[fishb0y]

If you fill slow enough that you don't significan't raise the temp of the outside of the tankt hen you won't see much of a difference unless the water bath is cooled but that's an awfull slow fill. Even a very slow fill will warm the outside of the tank if you're putting very much air in.

You will get a better fill every time by performing a slow fill. You are right, a tank that is done on a slow fill will get warm. There is nothing wrong with topping up after a bit.

I just think you are over estimating the ability of water to cool down a tank. I understand heat transfer and fluid flow, I work on a nuclear reactor. There is a "film" of water that will reduce heat transfer between the tank and the water, without the circulation of the water that film is larger. Without a large temperature difference, you will not see as much transfer of heat out of the sides of the tank. As you said earlier, simple physics. Doesn't matter if it is a nuclear reactor or a Al80.

It all boils (note the pun) down to this... If you want to jam a tank then you will get a poor fill, with or without a water bath.

 

[MikeFerrara]

On wet fills - http://www.psicylinders.com/library/Current/wetfills.htm

The author is Bill High, The guy who wrote the book, standards, and procedures that visual inspectors use.

DM

From the article...

Reported Water Tub Benefits
Several perceived benefits to using a water bath during fill are offered by tub proponents.

They include (1) cooling allows more air in the cylinder, (2) cooling allows faster fills, (3) the water will absorb the energy of a ruptured cylinder, (4) the tub itself provides explosion protection, and (5) the water bath provides cylinder cleaning.

Relating to benefit numbers one and two above, cylinders, when filled at the industry recommended fill rate of 300-600 psig/min, do not get hot. They may be warm but usually the temperature of the water is too close to the cylinder increase (about 100 to 110 degrees F. maximum) that the exchange rate is slow and low.

Our shop room temp was regulated to about 75 deg year round and that was the temp of the water bath. 75 degree water will conduct heat away from a 110 degree object 20 times faster than 75 degree air. PERIOD.

Additionally a 600 psi fill can get a tank REALLY warm even what some might call hot. Even filling off of our 5 cfm compressor before we had a bank system got tanks darned warm and that isn't even 300 psi/minute in an 80 cu ft tank. Don't believe me. try it. take a set of steel 104's and fill them from 500 psi to 2640 or a set of HP tanks to 3500 and feel the tanks.

We don’t want more air in the cylinder than is allowed by law. We don’t want fast fills, beyond the industry standard, if for no other reason, than cylinders will get warm and such practice makes the air station un-defendable.

No, we don't want fast fills or over filled tanks and niether was our goal.

The whole water tub thing began in the mid 1950’s when we knew very little about cylinders and their care. Steel cylinders got warm during what we now know to be fast fills. We didn’t know about prudent fill rates, and we often ignored the service pressure limit. Cylinders were filled quickly, removed from the water promptly and very little actual in-water temperature reduction took place. Then along came aluminum cylinders with walls nearly ½ inch thick.

The aluminum cylinders didn’t seem to get as warm. That was because although we still filled quickly, the heat generated within the cylinder took much longer to transfer to the outside. The water bath cylinder was removed from the water and sent on its way, long before the fast fill generated heat could be dissipated into the water.

True but we use lots of steel tanks, we do know about prudent fill rates and we don't ignore pressure limits and we do not always remove the tanks from the bath before the bath can help though really it doesn't matter because all things being equal the water will conduct much more heat away that air.

Additionally, he didn't mention the advantages when PP blending. For example, when blending trimix we add helium VERY slow with a digital controller to limit heating as much as possible. We let it cool and top as required and if you are fussy you'll be topping no matter how slowly you fill. Then we add O2 VERY slowly keeping the fill rate below 60 PSI/minute using a the same digital controller. again we let cool and top as required. Lastly we top with air. grated with practice you can get consistant results by learning what kind of fudge factors are needed with your equipment and fill rates but the water bath reduced heating and the necessary cooling time which produced more accurate mixes in less time. No fast fills and no overfilling. In fact at home, since we have the time, we often fill He one day, O2 the next and top with air the next. Not always but often. With some mixes it doesn't matter if you're off a bit but when you get to mixes with a really low FO2 that's no longer true.

Again, you can get good at hitting your mixes without the water bath and without waiting for cooling (by tossing in some fudge factors) but allowing cooling time takes the guess work out and a water bath reduces the time necessary.

The water bath makes a differnce. Whether the difference is worth the trouble of a water bath is up those who own and/or fill the tanks. I decided that it wasn't worth the trouble but to suggest that there isn't a difference is demonstrably false. LOL

 

[Thalassamania]

Find an LDS that knows what it's doing.

Unless my calculator use it off, to wind up at room temperature and 3443 PSI the tank at 5000 psi would have to contain gas at 320 degrees F.

 

[ScubaKris]

In the mid 80's, Bill High certified myself in a small group, in honolulu, HI. I thought he was a great guy, very knowledgable, he knows his stuff. He would tell use stories of when he learned to dive in WWI while stationed in a little known place called Honolulu. At that time he traveled the country as a professional witness for compresed gas accidents. For years we emailed back on forth. I have not heard from him since about 2000.

He made the statments then about not using the water bath. Even though I has great respect for him, I disagreed with him 20 years ago and I still do on the water bath.

I don't use a water bath. One tank at a time at 3.5 or 4 CFM does not make any noticable differnce

 

[Tom Winters]

Years and years ago, there was a shop on Oahu that used a chilled-water bath for tanks. Fills took 30 seconds or so and the surface of the tank never changed temperature that I could notice. The water was numbingly cold.
10 tanks took maybe 5 minutes - attaching the valves and handling the tanks took longer than the actual fill.
Ambient water baths are a waste of time. That's just my personal opinion. Superchilled though was awesome.

 

[MikeFerrara]

I dive the local springs a few miles from my property in Florida often, Morrison, Vortex, Cypress. I see people getting upset when their fill is onlly 2999 when it should be 3000. The new guys normally get stuck on tank fills for the day at Vortex and won't fill one over 3000. Heck, when I come back and put a tank on the compressor, when I check it, anything over 2500 I pull it and put on another,. I still often surface with 800psi. If your air margin is that tight, ..get a bigger tank.

I can't even read down to 1 psi on my SPG but I don't see anything wrong with expecting a tank to be pretty close to full when you're paying for it.

My dive plan, gas plan or anything else about how much gas I need or why I need it just isn't up to the fill station oporator. All they need to do is give me the fill that I'm paying for.

 

[MrBill_FTL]

HELLO!

I did my first dive with my x7-100. really nice day. sea less 1' clear. good vis.

well, the tank had almost 4000psi, to start... used about 1000, in 45min. and had it topped to 3400 at padi shop,

I guess if I was a techical/cave diver I'd want to pump these up to 4000psi, but 3400 seems fine...... after all its a 100 cft! eh?


My 1st impression is its heavy! too much for my BC!, so had to pul 5lbs out. just to keep it floating... will see at end of dive if 4lbs is enough...at end of dive... I may go up and get a belt, since it only 15-20 feet...



So, other than working on the correct weight to reduce/transfer from steel to Al, I'm lovin the new HP steel.

 

[Hoosier]

I don't get what dry fill is.... Just pump up 5000 psi and cool down....?!?!?!

 

[Dive-aholic]

I don't get what dry fill is.... Just pump up 5000 psi and cool down....?!?!?!

Dry fill is filling tanks without putting them in a water bath. The 5000psi thing was either a typo or the words of a tank monkey that doesn't know any better.