Tank Pressure and Volume

[BigTuna]

I guess I'm looking for the volume at, say, 3000 psi overfill for a standard 95 CF tank vs the 2640 overfill.

I'm a little late on this thread and might have missed it, but there's a sometimes confusing point about the ratings of LP steel tanks. A LP tank contains its rated volume of gas only when the pressure equals the rated pressure PLUS 10%!

Using your example, assuming the 95 CF tank is a low pressure tank rated at 2400 psi, it will contain 95 CF only if it is filled to 2640 psi (that's 2400 plus 10%).

To find out how much gas it contains at other pressures, use the formula already provided and multiply the ratio 95/2640 by the pressure of interest. Here are some numbers for the example tank:

86 CF at 2400 psi (rated pressure); 95 CF at 2640 psi (rated volume, and rated pressure plus 10%); 101 CF at 2800 psi; 104 CF at 2904 psi (rated pressure plus 20%), 108 CF at 3000 psi. Try the calculations yourself and see if you can reproduce some of these numbers.

In my experience with LP overfills, I request 3000 psi, but what I get after the tank has cooled seems to be around 2800. For the example tank at 2800 psi, that's 6 CF (6%) more gas than the rated amount.

 

[Caver95]

SWEET JEUSE, all you people overfilling those tanks of yours are going to get arrested and sent to jail and become the wife of some 300lb killer.

 

[BigTuna]

SWEET JEUSE, all you people overfilling those tanks of yours are going to get arrested and sent to jail and become the wife of some 300lb killer.

The same tanks are reportedly rated higher in Europe and used without problems. Besides, the history of explosions of LP tanks is virtually non-existent, as best I can tell.

 

[Tom Yerian]

Ignoring the percent or two error caused by air not being an ideal gas the free volume of gas is just proportional to pressure.

Current Volume = Rated Volume * (Current Pressure/Rated Pressure)

Example: A tank that has 108cu ft at 2640 psi will have 108/2640*3000= 122 cu ft at 3000psi.

Using that same formula, and you want pump your tank to, say 3500 psi...

108/2640x (new working pressure)....108/2640x3500= 143.1 cft3. Say that same tank has 1700psi, and you want to know how many cft3 you have in it, in case you need to make another dive...108/2640x1700 = 69.5 cft3. Taking into consideration the diff. between (rgl's and Igl's), it works both ways.Formulacft3/wp x nwp), or, Cubic ft.divided by working pressure, times new working pressure. Hope this helps you a little... Capt. Tom

 

[Leadking]

The same tanks are reportedly rated higher in Europe and used without problems. Besides, the history of explosions of LP tanks is virtually non-existent, as best I can tell.

I will repeat the following statistics, that I seem to post on a monthly basis;

Faber makes no tank greater than 7 inches in diameter that can take 4000 psi under any regulation anywhere in the world

U.S.tensile strength for 3AA cylinders (105,000-125,000 psi) is not the same as European tensile strength (135,000-155,000 psi as required by EN 1964 part 1 and ISO 9809 part 1) and I have test data that shows Faber cylinders delivered to us show a tensile strength of 115,000-123,000 psi (as required by DOT)

You can verify my info my registering at www.divefaber.com and reviewing the stats yourself.

Go to PSI's website and view his comments on steel vs. aluminum. More steel cylinders have catastrophically failed than aluminum. Also talk to any hydro facility there are is about a 9:1 ratio of aluminum to steel tanks out there, so on a mathematical interpretation steels are much more likely to have a catastrophic failure.

 

[oxyhacker]

If you are going to repost that, then I guess I got to repost this:

However if you look at higher pressure, but not 300 bar tanks, you will find that Farber turns out numerous 8" diameter 15 liter 203 and 232 bar tanks to meet various Euro and world standards, that weigh within a few ounces of what the US 95 does. So while it seems clear that the US LP tanks are not relabled 300 bar tanks, the possibility that they may be a slightly modified 203 or 232 bar tank remains. However, even if this is true it is almost certain that there are differences in heat treating and maybe metallurgy, that makes it foolish to assume they are identical.

Also, if one compares the specs on the new PST tanks, one will notice that the 3442 psi E8-119 and 130, while closely duplicating the dimensions and water-volume capacity of the old 2640 psi PST 95 and 104, actually weigh about 3 lbs less! All of which tends to support the notion that the DOT-spec 3AA tanks are very conservatively designed.

I will repeat the following statistics, that I seem to post on a monthly basis;

Faber makes no tank greater than 7 inches in diameter that can take 4000 psi under any regulation anywhere in the world

U.S.tensile strength for 3AA cylinders (105,000-125,000 psi) is not the same as European tensile strength (135,000-155,000 psi as required by EN 1964 part 1 and ISO 9809 part 1) and I have test data that shows Faber cylinders delivered to us show a tensile strength of 115,000-123,000 psi (as required by DOT)

You can verify my info my registering at www.divefaber.com and reviewing the stats yourself.

 

[RAD Diver]

I sure hope you have a greater respect for the other limits involved in diving. Got DAN?

Actually I do have DAN & do respect the other aspects of diving, but when you dont know everything ( which I admit I dont ) & you get different opinions from everyone that should know then what do you do? Im not filling these tanks.
I do not get them to 3300 always, but 2800- 3000 seems to be the norm.

 

[Leadking]

The argument that DOT is to "conservative" does not hold air. Plese review the metalurgy in my post. The test data shows that you CANNOT have a DOT cylinder and a European cylinder meet the same tensile yield.

The new Worthington's we are building more closly meet the European metalurgy, that's WHY they are 3442 psi rated (and given an exemption from the DOT)

 

[oxyhacker]

You got the wrong guy - my point has never been that the Euro and DOT tanks are identical! Just that they are not as completely different as you would have it.

I have always acknowledged that there are differences in heat treating, and often, metallurgy. However it is really hard to say just how significant these really are. The fact remains though, that the DOT 3AA spec tanks have shown themselves to be extremely reliable in service, even when routinely overfilled, which I think adequately demonstrates that they are very conservatively designed.

Anyhow, hopefully we'll be able to put the whole overfilling agument behind us before too long. The new 3442 psi tanks let the user have his/her cake and eat it, and the DOT has been working with the ISO towards a new set of metric international cylinder specifications which will allow US and overseas manufacturers to build tanks to the same "performance-oriented" (which seems to mean, less conservative) specs.

The argument that DOT is to "conservative" does not hold air. Plese review the metalurgy in my post. The test data shows that you CANNOT have a DOT cylinder and a European cylinder meet the same tensile yield.

The new Worthington's we are building more closly meet the European metalurgy, that's WHY they are 3442 psi rated (and given an exemption from the DOT)

 

[Leadking]

My post was directed at "Big Tuna".

None the less you are correct in that DOT and ISO working on a world standard, it is the U.N. spec and will allow a cylinder to be filled in all signing parties countries but as the say "don't hold your breath"

thanx,

Lee