Comparing Small SCUBA Cylinders

[Jeremy Williams]

I'm not really attempting to re-hash the various arguments for size. I just wanted a better look at the specs, and after looking I thought it might be worth sharing. There are some small differences.

Metal Impact
Scuba Cylinders | Metal Impact
Catalina
High Pressure Aluminum Gas Cylinders | Composite Cylinders - SCUBA Aluminum Cylinders | Composite Cylinders | Impact Extrusions
Luxfer
L6X® aluminium SCUBA cylinders
Faber
Blue Steel Scuba - Cylinder Specs

Note that the length of the MI AL40 just has to be wrong on their web page at 14.6 in. I used a secondary source instead. Also, MI doesn't seem to provide internal volume for some reason. I really dislike that but I didn't call to ask for additional specifications and I wasn't able to find it from an alternate source. All specs are (supposed to be) without valve.

Here is what I found...

Calculated Capacity = Internal Volume (in3) * Service Pressure (psi) / 1728 (convert inches to feet) / 14.6959 (1 ATM)

Here is what I see...

1. The Luxfer AL19 surprisingly carries about 5% more gas than the competition in that nominal size with about 5% more overall length.
2. The two Faber steel tanks in this comparison do not seem to be commonly used as stage/pony/deco cylinders and seem more commonly used with rebreathers. I believe that there is no technical reason for this, but they have the general disadvantage of higher initial cost than an AL tank. Also, there doesn't seem to be a generally available tank boot for them which adds an operational challenge.
3. The Faber steel HP23 provides more gas at similar dry weight to an AL19, but in a slightly narrower and longer form factor with potentially more desirable buoyancy. The higher service pressure may be viewed as a disadvatage and a 'short' 3000 psi fill yields similar gas capacity to the Luxfer AL19.
4. The Faber LP27 sits between the AL 19 and the AL30 in capacity, but in a form factor that is much shorter than either. This may be helpful to people who aren't tall or potentially to people who fly with cylinders. This is the only cylinder that has a larger nominal capacity than it's calculated capacity, which I think is rather odd. Are people doing unintentionally liberal gas planning calculations using a 27 cubic feet capacity with that tank? Or just overfilling them to 3000 psi?
5. In the AL30 and AL40 size, the Catalina cylinders are about a pound heavier in dry weight. I assume that's intentional since I believe these are all using very similar 6061-T6 alloys. Advantage or disadvantage, depending on your point of view. If used for deco/stage, it's less positively buoyant when empty. If used as a pony it's just more weight to move around.

Did I miss anything?

 

[Wookie]

The Fabers are indeed rebreather cylinders and are steel, making them desirable for a rebreather and undesirable for much of anything else.

I've never heard of a Metal Impact before this very minute.

The Luxfer and Catalina are close in size and capacity, but the Catalina don't hang right when they are slung and empty.

What are you trying to derive from this data?

 

[tbone1004]

what are you trying to actually get from this comparison? i.e. what application?

2. it also has to do with buoyancy characteristics. The steels are quite negative compared to the aluminums and are heavy enough to throw your trim off. Not enough gas volume for any open circuit stage or deco so they are relegated to onboard bottles for CCR.

3. you want pony bottles to be as light as possible in the water, but it is their full buoyancy that matters. For that, AL40's are by far the best bottles to have around for deco use because they are less than a pound negative when full so as a pony bottle they basically disappear, and as a deco bottle they do the same. Not enough gas volume for stage bottles, and AL80's are much better suited for that.

4. on rebreathers, the 27's are rarely used *O2ptima being the only one I can think of that uses it as standard* and those bottles are filled to 3600psi in cave country for dil, and usually up to 3000 for oxygen. It is too short and fat to be useful as an open circuit bottle.

5. you want them to be as floaty as possible so Luxfer is what you normally see.

@Wookie Metal Impact is Worthington aluminum btw.

 

[Jeremy Williams]

I'm not working towards a specific use case. I just wanted to understand the differences between the "same" aluminum cylinders. The original thought being whether it mattered which brand you get. I hadn't paid much attention. I was a bit surprised at the differences and similarities. A lot of posts tend to jump in the same direction (AL40!) and the discussion of the relative differences get lost. It would be fun to have one of each so you could try them all, but that just isn't practical.

I added the Fabers because I thought they were interesting. They are a unique size, but that's what's available. And only barely available in the case of the LP27s. I agree that the LP27s are pretty exotic. I hadn't noticed them myself before poking at this.

@Wookie I think the idea that you don't prefer a slung Catalina is interesting. I assume that's AL30/40 size? Comparing the two, what's 'wrong' about the Catalina?

 

[Wookie]

I'm not working towards a specific use case. I just wanted to understand the differences between the "same" aluminum cylinders. The original thought being whether it mattered which brand you get. I hadn't paid much attention. I was a bit surprised at the differences and similarities. A lot of posts tend to jump in the same direction (AL40!) and the discussion of the relative differences get lost. It would be fun to have one of each so you could try them all, but that just isn't practical.

I added the Fabers because I thought they were interesting. They are a unique size, but that's what's available. And only barely available in the case of the LP27s. I agree that the LP27s are pretty exotic. I hadn't noticed them myself before poking at this.

@Wookie I think the idea that you don't prefer a slung Catalina is interesting. I assume that's AL30/40 size? Comparing the two, what's 'wrong' about the Catalina?

I have some of all of them in 40 cubic foot size. Many in the 13 and 19 size, I have 2 and 3 liter Worthington steels, 2 and 3 liter faber steels, 13 and 19 Luxfer aluminum, and 40 Luxfer and Hy-mark.

I thought Worthington's aluminum line was Hy-mark?

 

[Wookie]

I'm not working towards a specific use case. I just wanted to understand the differences between the "same" aluminum cylinders. The original thought being whether it mattered which brand you get. I hadn't paid much attention. I was a bit surprised at the differences and similarities. A lot of posts tend to jump in the same direction (AL40!) and the discussion of the relative differences get lost. It would be fun to have one of each so you could try them all, but that just isn't practical.

I added the Fabers because I thought they were interesting. They are a unique size, but that's what's available. And only barely available in the case of the LP27s. I agree that the LP27s are pretty exotic. I hadn't noticed them myself before poking at this.

@Wookie I think the idea that you don't prefer a slung Catalina is interesting. I assume that's AL30/40 size? Comparing the two, what's 'wrong' about the Catalina?

I don't think anyone prefers to sling a Catalina. Either an 80 or a 40. They don't hang right.

 

[guruboy]

DGX recently started selling MI tanks. Had not heard of them before that.

 

[Kharon]

The two Faber steel tanks in this comparison ... there doesn't seem to be a generally available tank boot for them which adds an operational challenge.

I have a boot on my Fab 27. Got a generic somewhere. Don't remember where.

 

[tbone1004]

I have a boot on my Fab 27. Got a generic somewhere. Don't remember where.

the 27's are the same diameter as lp50's so you can use those boots on them with no issue

 

[2airishuman]

1. The two Faber steel tanks in this comparison do not seem to be commonly used as stage/pony/deco cylinders and seem more commonly used with rebreathers. I believe that there is no technical reason for this, but they have the general disadvantage of higher initial cost than an AL tank. Also, there doesn't seem to be a generally available tank boot for them which adds an operational challenge

They are negative when empty, which is undesirable because it increases the chances of losing a cylinder, and leads to more lopsided trim. The ideal small cylinder is slightly floaty when empty, so that it is more or less neutral with a valve, reg, and some gas. They must be filled to 3442 to get the added capacity, which isn't always feasible.

1. The Faber LP27 sits between the AL 19 and the AL30 in capacity, but in a form factor that is much shorter than either. This may be helpful to people who aren't tall or potentially to people who fly with cylinders. This is the only cylinder that has a larger nominal capacity than it's calculated capacity, which I think is rather odd. Are people doing unintentionally liberal gas planning calculations using a 27 cubic feet capacity with that tank? Or just overfilling them to 3000 psi?

They are similar to the now-discontinued PST and Worthington LP27s. I don't know whether those actually held 27 cf or not, but I would guess they did. Anyway, they're out of vogue now, because people have more or less standardized on AL40s.

Did I miss anything?

Usually trim comes up in these sorts of discussions. People seem to like the way AL40s float. I use an AL19 so I don't know from personal experience.

There are still some little HP Worthingtons out there. I have two of the HP40s and an HP11. I use them less and less. The HP11 is nice for soaking regs.