Dry Fill?

[MrBill_FTL]

Hello,

I just ordered a x7-100 hp steel tank. the shop tells me they dry fill the tanks to like 5000 psi, but they cool to 3400.

is this ok?

the description she gave made some sense.... that a tank in water would tend to absorb condensation.

also, she said do not paint the tank... (is this also true?)

I was thinking of some day glow spray paint... to help visability underwater.

what can I use if I dont paint it?

thank!

 

[BSea]

I don't know about the 5000 thing. It's true that the tank does lose psi when it cools down, but I've never heard of doing this. My LDS fills to about 3500, lets it cool for at least an hour then tops off. When you pick up your tank, they top it off again. Of course if you want your tank right away, then when it cools, you won't have the greatest fill.

I've known several people who painted their tank, but some places won't fill your tank if it's painted. You can always put on a scuba hide. I use reflective tape to give my tanks a little personality. Plus it makes them easy to identify, and makes me easy to identify underwater.

 

[Mark Vlahos]

Hello,

I just ordered a x7-100 hp steel tank. the shop tells me they dry fill the tanks to like 5000 psi, but they cool to 3400.

is this ok?

the description she gave made some sense.... that a tank in water would tend to absorb condensation.

also, she said do not paint the tank... (is this also true?)

I was thinking of some day glow spray paint... to help visability underwater.

what can I use if I dont paint it?

thank!

Filling cylinders that are not in a water bath is a good idea. If your cylinder is in a tub of water there is a greater chance that some amall amount of water could get in the valve and eventually into the cylinder.

The best way to fill a cylinder is slowly, if they plan to fill it so fast that when hot the pressure is 5000 PSI and that same cylinder will cool to a pressure of 3442 PSI then they are filling it way too fast. Fill it slowly and wait a while. It may require one or two top offs to get it up to the end pressure and it would probably be fine to go over the rated capacity a little, but from 3442 to 5000 is too much.

As far as paint is concerned, yes, do not paint your cylinders. Those Worthingtons don't need paint. If you do paint them just plan on the paint chipping off all the time. The end result will be that the cylinders look crappy and you will be putting paint chips in the water and every where else the cylinders go.

If you must make your cylinder more identifiable try stickers or tape. These will need to be removed every year when you get the cylinder inspected but they will be scratched and torn by that time any way.

Mark Vlahos

 

[spectrum]

She is an idiot, except for the don't paint part.

As Mark said slow gentle fills are the way to go. Top offs and perhaps a slight overfill will get you where you need to be. I have never seen a need to do more than a 10% overfill on a reasonable fill. 5000 PSI is crazy, that is almost hydrostatic testing pressure for that cylinder.

Filling in a water bath will make a good fill easier but at the risk of getting some water in your cylinder if the valve or whip gets wet.

The water bath is irrelevant for condensation. You will get more condensation when you take that cylinder down into cold water during your dive. Condensation is caused by bringing a mass of air down to it's dewpoint. Nothing is absorbed though the cylinder.

Don't paint any of the hot dipped cylinders. No good can come from it and they will soon look like crap. The weathered gray of the galvanized finish is a beauitful thing.

Pete

Hello,

I just ordered a x7-100 hp steel tank. the shop tells me they dry fill the tanks to like 5000 psi, but they cool to 3400.

is this ok?

the description she gave made some sense.... that a tank in water would tend to absorb condensation.

also, she said do not paint the tank... (is this also true?)

I was thinking of some day glow spray paint... to help visability underwater.

what can I use if I dont paint it?

thank!

 

[akscubainst]

Using her theory and rough calculations then she'd heating your tank to about 400 degrees F.

a rough estimate is that a tank will gain or lose 5 psi per degree F. Fill pressure on the tank is based on 70 degrees F.

So if your tank is full at 3442 psi and 70 degrees and she pumps it to 5000 psi the only way it will cool and drop 1,558psi is by dropping 311 degrees.

Most tanks will heat up to about 100 maybe 120 degrees during the fill so they will drop 200psi or so when they cool. Slower is better.

Dave

 

[pescador775]

Mr Bill,
You have received some good advice. About the water bath, some dive shops decided it is too much trouble to use a water bath. They put pressure on some groups (oops, "agencies") to prepare position papers which is a high falooting way of saying propaganda-- the purpose of which was to provide a politically driven rationale for blessing what the shops were going to do anyway, eg keep the customer milling around the shop for a 1/2 hour or more while a slow fill is underway. Whether slow fill or fast is the choice, some go for the dry, fast fill, or hot fill, leading to over pressuring the tank. The best argument that the group(s) could come up with was to say that water tanks are a source of internal tank rust. My opinion is that water baths are useful for fast fills and for accurate fills. Furthermore, exclusive of some old aluminum alloys, a 3-5 minute wet fill is not harmful but saves the customer time, and avoids aggravation due to the final pressure being way low as sometimes happens with hot fills. As far as rust due to water bath, normal care is expected when handling life support equipment. I mean, if you can trust these people to fix your regulator, why can't you trust them to jam your tank?

 

[Dive-aholic]

Did she mean 4000psi? The most I've seen tanks lose when cooling is about 500 psi. If they are really filling to 5000psi, then you better get your burst disks changed every few fills. They're really going to take a beating. If you want to make your tank stand out without painting it, buy a tank decal. You just stick it on the tank. They come in some pretty wild designs.

 

[Nemrod]

Tanks should be filled in a water bath. It takes no effort to clear the whip and the valve of water. Circulating cool water gives a solid fill much quicker than the dry fill crap which is propaganda. The water does not cause internal condensation unless there is moisture in there to begin with and it does not cause the metal to recystalize or rust or weaken or anything else that these new propagandas extort to justify being lazy and CHEAP. I call BS. N

 

[Dive-aholic]

I fill my tanks dry at home with a nice slow rate. The most pressure I lose is 50 psi. Sure, it takes 15 minutes to fill a single AL80 and 35 minutes to fill my doubles, but I get good fills. All water baths do is pull the heat away from the tank faster. You still have to fill slowly and then leave the tank in the water until the temperature equalizes. I'd rather just slow down my fill rate.

 

[MrBill_FTL]

WOW great response... THANKS!!! :bang:

I just picked up the tank. came w/ boot and cap.. and fill...

They said not to paint the tank and avoid stickers as the salt wants to penetrate the galvinaizing. I think it will be harder to see underwater...

first impression, its small.. I could have got a 120...
the 100 is taller than my AL 65 and shorter than AL 80.

the place I picked it ups
seemed like they had a very knoledgeable staff... off the beaten path, and very busy... real nice rental stuff...

so, I probably got it wrong...

but it sure sounded like they know hot much to over fill to get that 3400psi target.

sounded dangerous to me... think I'll wait outside when they fill them.. LOL!

just curious, what should I expect to pay for a HP fill? think I pay $6 for the AL80. (less with a air card)