Tank fills

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ScubaNorth

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I came across this article on the web and thought it might be of interest. I have had my tanks filled at a wet fill LDS and a dry fill. I always figured the store performing a wet fill was doing a better job (maybe because the staff is excellent so I am biased) and the dry fill LDS was just ill equipped (maybe because the staff is not excellent). After reading this article I am sold on dry filling.

http://www.naui.org/pdffiles/tankfill.pdf
 
Thanks for posting this. I had received a bit of the pro-dry story at SS Divers in Weymouth, now I have the whole story. They'll really love me when I raise the issue at North Atlantic's wet-fill station.
 
yak:
Thanks for posting this. I had received a bit of the pro-dry story at SS Divers in Weymouth, now I have the whole story. They'll really love me when I raise the issue at North Atlantic's wet-fill station.


While I only go SS Divers these days because 1.) They fill NITROX - [unlike NAS where they "don't belive in NITROX"] 2.) They actually know something about tech diving and don't take cheap shots at gear configurations they don't understand 3.) I like looking at Al's Inspiration....I must say that for the years I went to NAS - they give the BEST fills and I never had any problems with my tank damage. All last summer I was diving with a buddy how goes to NAS - his hp fills were always 3,600-3,700psi on the dock, mine were always spot on at 3,400psi - it's not the end of the world, but it's nice to get a big fill, espically when it's $20 for doubles.
 
More on the hazards of wet fills here from Bill High at Professional Cylinder Inspectors - someone who could reasonably be called an authority on the subject.
 
Good article. I never knew the aluminums had a heating problem to begin with. It seemed to me to be only steel. In Europe and cave city, its common to way overfill steel tanks a practice that is bad. When you buy a used steel tank, make sure it wasn't owned by a person who may have overfilled it for years or had a habit of overfilling it. Ask questions.

Chris
 
ScubaSarus:
Good article. I never knew the aluminums had a heating problem to begin with. It seemed to me to be only steel. In Europe and cave city, its common to way overfill steel tanks a practice that is bad. When you buy a used steel tank, make sure it wasn't owned by a person who may have overfilled it for years or had a habit of overfilling it. Ask questions.

Chris

Lots of people have overfilled steel tanks for years and years - I don't think it's 100% clear that it's "bad." All the horror stories I've heard have been with al tanks (like the fatal accident in FL this year) and steel tanks where people have done crazy stuff like paint them on their own.

From what I've read (in, for example, "The Oxyhacker's Handbook" overfilling steel tanks (lets say LPs steel to 3000 or 3500) will result in the tank failing hydro in something like 20 years instead of 30 or something extreme like that. I don't see a problem with overfilling lp steel tanks. Of course, I would never want to overfill and AL tank and with hp tanks I'd be concerned about beating up on my regs.
 
MASS-Diver:
Lots of people have overfilled steel tanks for years and years - I don't think it's 100% clear that it's "bad." All the horror stories I've heard have been with al tanks (like the fatal accident in FL this year) and steel tanks where people have done crazy stuff like paint them on their own.

From what I've read (in, for example, "The Oxyhacker's Handbook" overfilling steel tanks (lets say LPs steel to 3000 or 3500) will result in the tank failing hydro in something like 20 years instead of 30 or something extreme like that. I don't see a problem with overfilling lp steel tanks. Of course, I would never want to overfill and AL tank and with hp tanks I'd be concerned about beating up on my regs.
I have a reference text which indicates that according to PST(Pressed Steel Tank company) overpressurization may cause cumulative and irreversible damage.
DOT regulations stipulate that compressed gas cylinders are not to be over filled i.e. its illegal to overfill. With this being the case, if there was an incident in which an overfilled cylinder burst and caused damage or harm, the liability position would be untenable for the shop or operation that did the fill.

BTW, the article in the NAUI link in post #1 was published in Nov/Dec 1988.
 
Old cave country joke: If you're diving Pressed Steel LP tanks, how do you know when it's time to turn the dive? When the tanks are full...

All the DOT rules and lawyerese about the perils of overfilling LP steel tanks is challenged by the fact that there have been so many people doing it for so many years. It's a "bad" thing to do, but probably doesn't qualify as "evil." Aluminum tanks are a different breed, however - seeing the paint stretch on those things would give me the willies.

I don't know of any shops in my area that will overfill, but I know a whole bunch of homebrewers that routinely puff their tanks up until they squeek - and I'm not hearing lots of loud explosions or seeing body parts flying through the air. I'm not saying it couldn't happen, just that it doesn't.

To bring this thread sort of back on topic, if you have to fill wet so that you can dissipate the extra thermal load that comes with overfilling, you should consider slowing down or maybe closing the valve at the rated tank pressure.
 
The stories I've heard (and they are stories no actual proof by me) are of divers doubling up the burst disks or putting in plugs then double filling the tanks. If you buy off ebay used steel etc you may end up with one of these if the story is true and not know until a hydro or 2 later and hopefully not an explosion.

Chris
 
You'll be hard pressed to actually prove it's actually illegal. I'm not saying it's a good idea to overfill, but making a blanket statement that it's illegal isn't correct.

jbd:
I have a reference text which indicates that according to PST(Pressed Steel Tank company) overpressurization may cause cumulative and irreversible damage.
DOT regulations stipulate that compressed gas cylinders are not to be over filled i.e. its illegal to overfill. With this being the case, if there was an incident in which an overfilled cylinder burst and caused damage or harm, the liability position would be untenable for the shop or operation that did the fill.

BTW, the article in the NAUI link in post #1 was published in Nov/Dec 1988.
 

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