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View Full Version : 95cu.ft. steel LP, 3000-3500psi?



BORG
12-31-2007, 17:57
I have a 95cu. ft. LP steel tank I've had about 8-9 years, current V.I. P. and hydro., like new interior.
I talked to my LDS recently and he said I could probably fill it(overfill) to 3000-3500 psi with no adverse effects.
What would be my cu. ft. of gas with 3000 and 3500 psi, respectively?

Also approx. how much would the filled weight increase on the tank at 3000 and 3500 psi. I'm wanting to know this for buoyancy reasons, of course.
Should I have the burst disk changed to safely handle the higher PSI on a regular basis.


THANKS!

cummings66
12-31-2007, 18:27
.0807 lbs per cf of air is the magic number you need to know how to answer your question.

You do not need to know this for buoyancy because it doesn't matter what your tank weighs when full, only when it's empty, the full one just weighs more at the start of a dive is all you'd notice.

So, figure up how many cf your tank holds and then you can figure out how much more it weighs overfilled by using the above figure to get it. ie if your 95 cf tank holds 95 cf at 3000 psi you can guess that you've got about 15 cf more gas. Now that would weigh about 1.21 lbs. To figure that and this applies to any tank, it's AOW knowledge that you should hopefully learn when you take your course, you take your tank capacity in cf and divide it by the tank pressure. This gives you a number that you can then use to tell you how many cf of air you have at any psi reading. You need to know this if you dive multiple tanks and want to know how much gas a dive would use, obviously your tank would have more gas than an AL80 and if all you know is your SAC in cf then you've got to know how to convert between tanks and pressures to make them equal.

So, I should note that not all tanks carry the amount of gas the tank label would seem to indicate, for example an AL80 does not contain 80 cf of gas. Without knowing what your tank is I don't know for sure how much it has, but I'm sure the final weight addition is still pretty close to 1 and a quarter lbs.

PS, good luck on the drysuit course and the AOW course you want to take. Drysuit is the most fun course I think, it's got it's ups and downs...

Matt P
12-31-2007, 18:38
My LDS regularly rents out LP 95's and over fills them, Generally to about 3200. In rare cases they'll take it to 3400.

BORG
12-31-2007, 20:59
Thank you for the info. I really appreciate it!

BORG
12-31-2007, 21:04
Thanks!!!!

awap
01-01-2008, 09:36
And the volume question: Your 95 cu ft tank is rated for 2640 psi so that works out to .036 cu ft per 1 psi (95 divided by 2640). Multiply time 3000 and you get 108 cu ft. Time 3500 and you get 126 cu ft.

in_cavediver
01-01-2008, 09:44
The only other point added is that if you plan to 'cave' fill them, you will need to change out the burst disc. I'll leave out any reference to moral or ethical implications. If you don't do it, you'll likely blow a disc.

BORG
01-01-2008, 13:46
I checked my original burst disc and it is stamped with 4000psi. on it.

BORG
01-01-2008, 13:48
Thanks for the info. I didn't what a versatile tank I had with my 95 LP.

in_cavediver
01-01-2008, 18:20
I checked my original burst disc and it is stamped with 4000psi. on it.

Yep, that's correct for the 2640 rated tanks. 3000 psi al 80's get the 5000psi burst disc. The 5000psi disk is what I'd use if I overfilled my LP 104's, That of course I never do. I let the dive shop do it for me!

CompuDude
01-02-2008, 02:33
I checked my original burst disc and it is stamped with 4000psi. on it.

Upgrade to a 5000 psi disk. Burst disks age over time, flexing as tanks are filled (or overfilled) and emptied and after 8-9 years, it's likely that burst disk is not longer quite as effective and probably won't make it to 4000 psi. One hot day with an overfill in your car, and you're going to end up replacing some car windows! (and changing your shorts if you're anywhere nearby)

Grin
01-02-2008, 07:21
I have a few LP85s and always get them filled to 3200-3400. I did have a disk blow once. Replaced it with a 5000lb disk. It blew at the dive shop when they were filling it. I think they thought it was a HP tank and were filling it to try to get 3600-3800 for the final fill. This would mean filling it to around 4000 so when it cools down it is around 3700. My AL 80s have 4000lb disks and the LP 85s came with 4000s. My HP tanks came with 5000 lb disks.

Jipps
02-04-2008, 10:29
definately switch to a 5000psi burst disk. just dont be like my friend, he replaced his burst disk with a stainless steel disk..we are pretty sure his valve will shoot off before the burst disk blows.

RoyN
02-04-2008, 10:46
I might be getting that for doubles.

BSea
02-04-2008, 10:48
definately switch to a 5000psi burst disk. just dont be like my friend, he replaced his burst disk with a stainless steel disk..we are pretty sure his valve will shoot off before the burst disk blows.That's just crazy. As long as he can buy burst disk, and replace them himself, there is no reason to plug an overpressure outlest. And that's what he's doing.

cummings66
02-04-2008, 13:53
That practice is kind of frowned on too. I'm not a fan of overfilling, but not because I think it'd dangerous. It's because I'm not convinced our tanks will last as long. I know lots that seem to be as old as the Earth itself so it's probably a moot point.

However, will your insurance cover it if something bad happens?

in_cavediver
02-04-2008, 16:36
That practice is kind of frowned on too. I'm not a fan of overfilling, but not because I think it'd dangerous. It's because I'm not convinced our tanks will last as long. I know lots that seem to be as old as the Earth itself so it's probably a moot point.

However, will your insurance cover it if something bad happens?

To be honest, you're right about the life span of the tanks. I likely will get 1/10th the life I could by overfilling them. Still, its in the thousands before it fails hydro.

I also don't much care for the double disking or SS disking of tanks. I at one time though it was AOK but after thinking a few things through, and noting the availability of 5000 and 6000 psi disks, there simply isn't a good reason anymore.

cummings66
02-04-2008, 18:59
I know some organizations advocate double disking as well, in fact a guy at my LDS double disk's his HP100's and fills them to 4000-4500 psi.

I don't agree with it, I think it's pushing things a bit too far.

newways
02-04-2008, 19:26
gue.com/Equipment/Config/index.html (http://www.gue.com/Equipment/Config/index.html)

It's a long read(great info) so I'll quote what it says under 'Valves" about halfway down.

"The benefits of bargain valves are questionable; therefore, divers should purchase valves of long lasting quality. Common favorites are Sherwood, Beauchat, Halcyon, and Scubapro valves.

Burst ports on valves and manifolds can cause serious problems if they fail. Should these release unexpectedly underwater, a diver would rapidly lose their available air supply. Technical divers typically replace these disks with higher-pressure plugs, which should be changed yearly along with the visual inspection of the cylinder."



Anyone ever heard of these discs being serviced yearly along with inspection?

cummings66
02-04-2008, 22:32
Yes, that's fairly common. GUE likes the higher pressure burst disks as well, I wonder though about that because it encourages overfills which I'm not a fan of.

WD8CDH
02-05-2008, 07:55
FYI, Most euro valves don't even have burst disks.

CompuDude
02-05-2008, 12:17
FYI, Most euro valves don't even have burst disks.

That doesn't mean it's a good idea.

Considering the silliness they're putting people through for something as simple as Nitrox over their, I hardly hold the Europeans up as a shiny example of how to do things. Although I like their choice in the DIN v. Yoke wars. ;)

WD8CDH
02-07-2008, 09:05
Not saying it is a good idea either. Just providing a data point.

cummings66
02-07-2008, 11:59
Interesting.