Tank fills- Wet or Dry?

[Waterlover]

I thought a little conversation on tank filling and which is best might be educational. Tell me how to do it.
Ken

 

[The Chairman]

PSI recommends that tanks be filled dry for a lot of reasons. It seems some shops are chilling the water to be able to "super-fill" tanks. The best piece of advice is to fill them S-L-O-W-L-Y... No, slower than that, @ 300psi/min MAX!!! It should take ten minutes to fill an AL80.

 

[roakey]

See: http://www.psicylinders.com/news.html

Roak

 

[Ed Jewell]

Checkout this site in regards to the dry filling of scuba tanks.

http://www.naui.org/pdffiles/tankfill.pdf

 

[budgy]

Filling cylinders can be a problem where it is hard to ever be right. If you are dry filling directly from the compressor, the medium size compressor I use, takes around 10 min to fill two 15 litre cylinders and gives you a hot fill. With room temp around 23C I expect a +-15% drop in pressure on cool down to room temp. There is no problem when you have time to top up a cooled cylinder to the correct W/pressure. If you want to take away the cylinder immediatly, some will overfill to just under the +10% max, or wet fill, to compensate. I am no expert but have read, rightly or wrongly that a Faber steel cylinder can be overfilled by 10% without exceeding the elastic limits and stretching the cylinder, though you are not supposed to fill above w/pressure.
If I take a 12.2 litre cylinder with 232 bar at room temp +- 23C and dive in the sea at around 6C, it seems I can expect a further rapid pressure drop to 217 bar, due to contraction.
Many of the steel cylinders I have sent for inspection are reported to have internal rust and I wonder what is the main cause of water entry and could I prevent it.

 

[Uncle Pug]

My real world tests in filling cylinders disagree with the theory of Fred Calhoun, PE that filling in a water bath is not effective.

I also find it interesting that Fred and Bill are arguing out of both ends when they say that *wetfills are not efficatious/wetfills result in overfilling*. Which is it fellas?

Well here is my experience. When filling two sets of double 104s off the compressor they will lose 15% if filled dry and will not lose any when filled wet. Time and again.

No Fred, you cannot eat my dry filled 104s.

 

[ebbtide]

i want my own compressor .
the place i get mine filled are at a fire dept in our town
they are filled dry but way to fast but it depends on who is filling them , they set the fill max psi to 3100 and by the time i get home and the tank cools down beacuse of the fast fill ive only got 2400 to 2800 psi in the tank , and this is y i want my own compressor so i can take my time filling them 15 to 20 min if i have to .

 

[Uncle Pug]

Originally posted by ebbtide
i want my own compressor .
the place i get mine filled are at a fire dept in our town
they are filled dry but way to fast but it depends on who is filling them

Back when I was a firefighter I would take a load of AL80s to work with me to fill while on shift. Even though I did the fills slowly I would still have them in a barrel of ice water during the process and never had any shrinkage or over pressurization when done and equilibriated to room temp. Dry filled the always shrank even when slow filled.

Is it possible for you to do the filling yourself? Or is this a courtesy the FD does for you but insists on doing the fills themselves?

 

[ebbtide]

they insest on fillnig them themselvs for insurance purposes and i dont blame them , it is there equiptment and it is expensive and i wouldent wanna ruin it !
so maby the wet fill would be more to my liken ? as i want to minimize the shrinkage as mutch as possible as we all know this canbe a real PROB *shrinkage * that is hahaha

 

[JustAddWater]

True, There is nothing like a hot fill to start your dive out on a bad foot.

"Wait it was 3000psi a second ago!"