Largest gas capacity aluminium cylinders?

[lowwall]

Because we are going to be kneeling on the sand doing underwater archaeology work we want to have the bailouts in a semi GUE style on the back - they won't be connected together or anything like that, but on the back gets them out of the way and leaves the arms totally free to move and it keeps the bailouts from potentially damaging anything. Its just a preference thing for this particular situation.

Minimum capacity is 3200 litres. So something like a 15 litre 232 bar cylinder would work. They are required for bailout cylinders for a project that is going to the same depth doing the same dive profile day after day after day.

How deep are you working? A minimum of 3200 liters for a bailout implies a lot of required deco.

The whole dive plan sounds questionable. We need more details, but based on just what you've told us, perhaps use a dedicated deco bar (bars?) hanging from the boat or whatever platform you are working from with second stages hanging from bottles on the surface. Even better if higher O2 mixes are available for use at the bar(s) for accelerated deco. Then for bailout, the divers would only need a standard pony that gives them plenty of time to get to the deco bar.

 

[RedSeaDiver2]

How deep are you working? A minimum of 3200 liters for a bailout implies a lot of required deco.

The whole dive plan sounds questionable. We need more details, but based on just what you've told us, perhaps use a dedicated deco bar (bars?) hanging from the boat or whatever platform you are working from with second stages hanging from bottles on the surface. Even better if higher O2 mixes are available for use at the bar(s) for accelerated deco. Then for bailout, the divers would only need a standard pony that gives them plenty of time to get to the deco bar.

Its actually 2x 3200 litre cylinders for bailout - one is 18/40, the other nitrox 50. Work on the sand is at 60 metres / 200 feet, if bailing out at the point of maximum planned bottom time then the first stop is at 30 metres / 100 feet. Deco bars will be deployed, however due to the at times vicious currents we aren't prepared to accept that a diver will be able to reach the deco bars when they need to every time, and so for that reason the divers will be carrying all required bailout gas with them.

 

[Tanks A Lot]

True - but they are a lot lighter than steels - which was the main thing that I was seeking. Unfortunately I haven't been able to find any full and empty buoyancy numbers yet.

There might be a bit of a misunderstanding: a steel cylinder will almost always be lighter than a comparable-sized aluminium cylinder.

While it is true that aluminium is less dense, the tensile and yield strengths of common 6061-T6 aluminium are roughly a third of those for the most commonly used chrome–molybdenum steels. In short, the walls must be about three times as thick. Put another way, you need significantly more material to make the cylinder, which negates any weight advantage aluminium might otherwise have offered. Looking at 11.1 litre cylinders rated for a working pressure of 207 bar makes this evident. This size is often referred to as an “S80” (a silly name, if you ask me...):

• Luxfer (Aluminium): 14.3 kg
• Catalina (Aluminium): 14.2 kg
• Faber (Steel): 11.9 kg

The lightest steel cylinder that tick your 3200 gas capacity from Faber are 12.0 liters cylinders at 300 bar. This gives you just above 3220 litres or so free air capacity at 20°C. These weigh 16.5 Kg.
ECS has a comparable cylinder at 17.0 Kg.

If you truly want a cylinder lighter than steel, composites are your only realistic option. On average, aluminium cylinders will always be heavier than a similar-sized steel cylinder. Given that only a handful of composite designs are even suitable for diving, the choice should be straightforward.

• Luxfers S106W has not enough free gas capacity for your needs. At 11.1 litres and 300 bar it only holds just under 3000 litres of air.
• You already found the Worthington composite, which offers the same gas capacity as the steels I mentioned above, while being considerably lighter.
• There are a handful more from companies I have no experience with at all.

From my limited experience with composites and inspecting them, I would like to point out that they are not nearly as rugged as a simple "common" cylinder. Especially when using these for heavy work, I would think carefully about their suitability. The fibers are much easier damaged than a steel or aluminium cylinder could ever be.
All of them are a pig to handle in the water as well, as they can be very floaty, which is something else to keep in mind. I know they seem appealing on paper, but once in the water and in use, things often don't look as good anymore.

If it was me, I'd probably look at 12.0 litre @300 bar from Faber. It's a rugged piece of gear that seems to fit the bill quite nicely. Faber makes the lightest steel cylinders as far as I'm aware. Otherwise, I would look at ECS, Vítkovice or others, there are plenty of steel manufacturers out there.

 

[lowwall]

Its actually 2x 3200 litre cylinders for bailout - one is 18/40, the other nitrox 50. Work on the sand is at 60 metres / 200 feet, if bailing out at the point of maximum planned bottom time then the first stop is at 30 metres / 100 feet. Deco bars will be deployed, however due to the at times vicious currents we aren't prepared to accept that a diver will be able to reach the deco bars when they need to every time, and so for that reason the divers will be carrying all required bailout gas with them.

So the divers are on rebreathers (presumably chest mounted) or surface supplied? Sounds like a complex project on what must be an important site to be worth the effort. I hope your findings are made available to the public once they are written up. Or sooner if you don't have to protect the site location.

 

[sea_ledford]

Because we are going to be kneeling on the sand doing underwater archaeology work we want to have the bailouts in a semi GUE style on the back - they won't be connected together or anything like that, but on the back gets them out of the way and leaves the arms totally free to move and it keeps the bailouts from potentially damaging anything. Its just a preference thing for this particular situation.

I figured it was archaeology work. Archaeologists like to think that what they are doing is completely unique and no one else does it the right way. I will give them that taking off fins and walking around the dig site as a better alternative to learning proper buoyancy control is a unique way of thinking... No dig on you, I've just worked with archaeologists before!

So is primary gas source CCR? Surface Supply?

 

[tmassey]

Humans like to think that what they are doing is completely unique and no one else does it the right way.

FTFY…

I figured this too. Not archaeologists per se, but a person in a new environment thinking about their desires and inherent assumptions masked as needs, and assuming they have the best handle on the balance of factors of their ‘highly unique’ ‘requirements’ ‘necessary’ for success.

175-200’ dives are really not that uncommon. I did 4 of them in a single weekend less than a month ago, and I’m a baby in that area of diving.

You ignore or reject the lessons of those experienced divers at your peril. Deeply consider Chesterton’s Fence: the concept that you should not come up with changes until you know why things are done how they’re done.

It’s not that you don’t have different needs or that there isn’t a better ways, because you might. Rather, it’s the idea that until you know the why of the current process, you’re more likely to *degrade* rather than improve the process.

The fact that you don’t understand why steels are preferred to aluminum tanks (they are often no heavier due to their superior strength and when you factor in the extra lead to get the tanks to stay negative are much *lighter* overall) leads me to believe you don’t fully understand the problem space yet.

taking off fins and walking around the dig site as a better alternative to learning proper buoyancy contro

Also not unique to archaeologists: *very* common for people for whom scuba is merely a tool rather than a focus — or maybe more accurately an *obstacle* to be subjugated quickly and without regard to anything else. Their goal is often to translate their current intuition and experience as directly as possible to the new environment.

Usually to their own difficulty, if not outright harm. The environment doesn’t care about your intuition…

 

[lowwall]

Its actually 2x 3200 litre cylinders for bailout - one is 18/40, the other nitrox 50.

I'm not a tech diver, but this sounds extremely dangerous. How are you going to verify that first breath at 200' is off the 18/40 bottle? It seems unlikely that you'll be able to follow standard verification procedures with back mounted independent doubles.

For example: How to Switch your Diving Gas

 

[RedSeaDiver2]

There might be a bit of a misunderstanding: a steel cylinder will almost always be lighter than a comparable-sized aluminium cylinder.

While it is true that aluminium is less dense, the tensile and yield strengths of common 6061-T6 aluminium are roughly a third of those for the most commonly used chrome–molybdenum steels. In short, the walls must be about three times as thick. Put another way, you need significantly more material to make the cylinder, which negates any weight advantage aluminium might otherwise have offered. Looking at 11.1 litre cylinders rated for a working pressure of 207 bar makes this evident. This size is often referred to as an “S80” (a silly name, if you ask me...):

• Luxfer (Aluminium): 14.3 kg
• Catalina (Aluminium): 14.2 kg
• Faber (Steel): 11.9 kg

The lightest steel cylinder that tick your 3200 gas capacity from Faber are 12.0 liters cylinders at 300 bar. This gives you just above 3220 litres or so free air capacity at 20°C. These weigh 16.5 Kg.
ECS has a comparable cylinder at 17.0 Kg.

Very true - it is a long time since I have had to really dial down into the specs of a cylinder.

If you truly want a cylinder lighter than steel, composites are your only realistic option. On average, aluminium cylinders will always be heavier than a similar-sized steel cylinder. Given that only a handful of composite designs are even suitable for diving, the choice should be straightforward.

• Luxfers S106W has not enough free gas capacity for your needs. At 11.1 litres and 300 bar it only holds just under 3000 litres of air.
• You already found the Worthington composite, which offers the same gas capacity as the steels I mentioned above, while being considerably lighter.
• There are a handful more from companies I have no experience with at all.

From my limited experience with composites and inspecting them, I would like to point out that they are not nearly as rugged as a simple "common" cylinder. Especially when using these for heavy work, I would think carefully about their suitability. The fibers are much easier damaged than a steel or aluminium cylinder could ever be.
All of them are a pig to handle in the water as well, as they can be very floaty, which is something else to keep in mind. I know they seem appealing on paper, but once in the water and in use, things often don't look as good anymore.

If it was me, I'd probably look at 12.0 litre @300 bar from Faber. It's a rugged piece of gear that seems to fit the bill quite nicely. Faber makes the lightest steel cylinders as far as I'm aware. Otherwise, I would look at ECS, Vítkovice or others, there are plenty of steel manufacturers out there.

The ones from Ace that you linked to Chinese and my experience with a lot of things from China is that they aren't really aware of what effects the end use will have on a product so I wouldn't necessarily believe that their cylinders are suitable for diving.

I'm keen to find out the buoyancy characteristics of the Worthington wrapped steel cylinders - they may represent the best balance between weight in air while not being too floaty. They don't have any buoyancy info on their website so I will send them an email to ask about that. If they are OK then 2x the Worthington Carbon Dive Cylinders will weigh about 11kg less than 2x the Fabers in the same size - which my back will thank me for.

 

[RedSeaDiver2]

So the divers are on rebreathers (presumably chest mounted) or surface supplied? Sounds like a complex project on what must be an important site to be worth the effort. I hope your findings are made available to the public once they are written up. Or sooner if you don't have to protect the site location.

Back-mounted rebreathers. Findings will be written up, and anything significant will be announced.

 

[RedSeaDiver2]

I figured it was archaeology work. Archaeologists like to think that what they are doing is completely unique and no one else does it the right way.

Same could be said about GUE

So is primary gas source CCR? Surface Supply?

CCR