Updated SCUBA tank specifications list -- in PDF and spreadsheet

[tmassey]

And in case it’s not clear: the PST E7’s *are* on the list. The 3500’s are not. But, also as stated, the epoxy Fabers are not on the list either when there’s a Faber HDG. Why? The differences are slight, so why confuse things.

I admit, the difference between PST 3442 and 3500 tanks are a little bigger, but still, not that much. PLUS I have no verified source for the info, and the Huron list doesn’t have water volume, either. So, that’s three strikes. They’re out.

Find a source, and if the difference is not within a few percent I would add them. But not otherwise.

 

[2airishuman]

Nice work, @tmassey. But, I'm a little disappointed that none of the older 3500 psi tanks are in the list. I have several PST E7 series 100 and 120 3500 psi tanks. They were in the Huron cylinder specs list.

I think it would be better to have a tank in the list, even if the spec source is the Huron list, than to not have the tank in the list at all.

They're the same cylinders as the 3442 PSI PST E7 series except for what's stamped on the shoulder of the cylinder and the size of valve they take, give or take manufacturing tolerances.

 

[tmassey]

They're the same cylinders as the 3442 PSI PST E7 series except for what's stamped on the shoulder of the cylinder and the size of valve they take, give or take manufacturing tolerances.

It's such unsubstantiated and unequivocal (and, I think, technically incorrect) statements that made me make the list in the first place! You hear things like that, but that doesn't make it true.

Here is a photo of two sets of doubles. The rear one is a PST E7-100 (3442) and the front one is a PST HP100 (3500). They are demonstrably different. Notice the clear line where the slope of the shoulder starts and the relatively sharp, flat angle of the HP's. Notice that the E7's are much more rounded. In the end, it makes about a 1/2" difference in height. They are also demonstrably different in *weight*, and that means that the actual blank used to form the thing is different.

And these are not "manufacturing tolerances". Notice that both 3500's are similar, and both 3442's are similar. They are clearly manufactured with slightly different techniques.

Now this may have less to do with the difference between 3500 and 3442, and more to do with the fact that the 3442's are 10+ years *newer*, and that E7-100's made 10 years after mine would be different, too, yet still be E7-100's. But it does not change the statement: there are differences between the two. And when you make categorical statements ('these are identical except for *tolerance* differences'), these differences show those statements to be categorically wrong.

But does it matter in reality? That's what I wanted to see for myself. Which is why I wanted as accurate information as I could get -- from the manufacturer. From everything I've been able to find, the differences are so small as to be meaningless.

But that continues for more than just the PST 3500 vs 3442 debate. Worthingtons have a reputation for being heavy tanks, right? Except when the Worthingtons are *lighter* than Fabers: see the HP100's; even when they are heavier, it's often a pound or less (out of 30+ pounds!). Of course, you have to read things correctly: often Faber tanks buoyancy are quoted *without* valves, when *everyone* else quotes it with. Add the change for a valve (how do you even *measure* a full tank without a valve!?!) and they're all right there with each other... (Of course, that opens up more questions: which valve did each manufacturer use? How heavy was it?)

Honestly, for me the biggest takeaway was this: the differences are slight. Don't get hung up on them. And don't take *any* number as gospel!

 

[tmassey]

But does it matter in reality? That's what I wanted to see for myself. Which is why I wanted as accurate information as I could get -- from the manufacturer. From everything I've been able to find, the differences are so small as to be meaningless.

Here's an item to reinforce this point: I added a column to my spreadsheet: Empty Weight per Tank Factor. It's simple: Empty Weight divided by EAN32 @ 3600PSI Tank Factor. It's a measurement of weight per 100 PSI of capacity.

You'd expect that tanks that vary as much as a 23 ft3 and a 119 ft3 tank would *have* to vary wildly, right? Nope. The vast majority of tanks are between 0.32 and 0.36, or less than a 15% variance. And the farthest outliers are at 0.29 and 0.40. I was *amazed* at just how consistent the numbers were! (Empty Weight per ft3 was similar but not as tight, which is why cave fills and tank factors exist.)

In short, don't worry too much about the numbers. Things like shape (long and skinny (e.g. HP120's) vs. short and fat (e.g. HP119's) make *much* more difference than trying to determine whether a PST 3500 is slightly heavier and less buoyant than a PST 3442 (or a Worthington HP100, or a Faber HP100).

 

[Matt S]

I think there's an issue with the numbers for the Metal Impact S080:

Metal Impact S80 3000 77.4 11.1 7.25 26.1 31.9 3.3 -1.5

The given buoyancy swing is only 4.8 lbs, not the 5.7-5.9 lbs given for the other 77.4 cf cylinders. I suspect this may be because Metal Impact quotes the "empty" buoyancy at 500 psi, and that gas should weigh just about a pound.

 

[2airishuman]

It's such unsubstantiated and unequivocal (and, I think, technically incorrect) statements that made me make the list in the first place! You hear things like that, but that doesn't make it true.

Here is a photo of two sets of doubles. The rear one is a PST E7-100 (3442) and the front one is a PST HP100 (3500). They are demonstrably different. Notice the clear line where the slope of the shoulder starts and the relatively sharp, flat angle of the HP's. Notice that the E7's are much more rounded. In the end, it makes about a 1/2" difference in height.

Those two cylinders are different. That does not mean they are different because one is a 3500 and the other is a 3442.

Also, although I understand what you are trying to do, I think it is a mistake to believe that any of the specifications are correct just because they came from the manufacturer. I mean, I have a bottle of the best scotch whiskey in the world. Says so right on the bottle, so it must be true, don't you think?

They are also demonstrably different in *weight*, and that means that the actual blank used to form the thing is different.

Perhaps your understanding of the manufacturing process is different than mine. I do not believe that cylinders are formed from "blanks."

And these are not "manufacturing tolerances". Notice that both 3500's are similar, and both 3442's are similar. They are clearly manufactured with slightly different techniques.

Now this may have less to do with the difference between 3500 and 3442, and more to do with the fact that the 3442's are 10+ years *newer*, and that E7-100's made 10 years after mine would be different, too, yet still be E7-100's. But it does not change the statement: there are differences between the two. And when you make categorical statements ('these are identical except for *tolerance* differences'), these differences show those statements to be categorically wrong.

I dunno. I think it shows that the manufacturing tolerances are much larger than is widely believed. There are some videos on youtube of the PST cylinder manufacturing process. It was not as precise or controlled as most people would expect it to be.

 

[SomeGuy509]

You design your manufacturing and set your specs such that even if you do a bad job making it the tank doesn't end up as scrap.

Dies wear out over time, may explain the difference shape for basically the same tank. New set of dies and they took the opportunity to tweak the design (cost, longevity, scrappage) .

 

[rjack321]

And these are not "manufacturing tolerances". Notice that both 3500's are similar, and both 3442's are similar. They are clearly manufactured with slightly different techniques.

No its the same method as illustrated here.

Basically a giant ram pushes a billet into a form. Then the neck heated is spun down. The whole thing is then heat treated and galvanized. There are cylinders which are spun from scratch (no ram to start the formation). Asahi is the only common company making cylinders that way. Worthington and PST and Faber have never made spun scuba cylinders.

 

[tmassey]

Also, although I understand what you are trying to do, I think it is a mistake to believe that any of the specifications are correct just because they came from the manufacturer. I mean, I have a bottle of the best scotch whiskey in the world. Says so right on the bottle, so it must be true, don't you think?

Don't worry about me: I got what I need. I now realize that the precision that people are trying to place on tanks is fairly meaningless. Not only is it very much 'Measure with a micrometer. Mark with chalk. Cut with an axe.' but even then, they all end up tightly centered around very similar parameters -- across the entire line of tanks! (That is, of course, leaving a very few weird tanks out of it; and *no* *one* should ever dive a spun tank.)

And I said it before, but I'll say it again: I'm not saying that these numbers are any more "right" than another set of numbers. But the numbers are demonstrably more *traceable* and *verifiable*. That *does* give them more credence--but doesn't make them more "right", and certainly not for *any* given specific physical tank.

What I dislike is the profound confidence given to provably-wrong statements. But given point #1 above, I no longer care about it. I'm just amused at this point.

I dunno. I think it shows that the manufacturing tolerances are much larger than is widely believed.

Those are not manufacturing tolerances. Those represent a change in the manufacturing process, and therefore producing a different revision. I have worked closely with several manufacturers who produce the same part over time. The number of changes that are made -- with actual, practical differences -- but are not told to the customer (or sometimes even the OEM) are startling, even frightening. But back to point #1: so not worth arguing about.

 

[victorzamora]

The one that irritates me more are the OMS tanks — and I don’t even own any of them. But they’re very popular in certain areas: it seems that 3/4 of Amigos rental fleet are OMS... . But with no manufacturer-supplied info... use the Huron list. You still have the Internet, right?

OMS tanks were made by Faber and rebadged. I can't remember all of the names, but the OMS tanks were usually called something slightly larger than the Faber/BlueSteel tanks. Like Faber LP108s are the same as OMS 112s. OMS125s are the same as Faber/Blue Steel LP121s.