Thinking Outside the Tank

[Herk_Man]

So, have had this thought running through my head for a long time. In today's day and age of carbon fiber products, why hasn't anyone produced a superstrong carbon fiber tank that can be filled to much higher PSI in a much smaller volume tank, than what we can get with steel or aluminum.

It just seems like you could develop something capable of 6000psi or so but small and light, that would give you the same amount of bottom time as current tanks.

I've what if'd this a bit.

CF does damage easier than metal but with the compact sized I'm thinking you could put bottom covers and some protection on it that would keep it from getting damaged.

May have some issues with the resins used for binding the CF but I'm sure that can be engineered if it is an issue at all.

Might have some problems with the ability of the vessel to handle bending moments where the valve connects to it, but this might be solved by having a hybrid type of setup where the cap is aluminum.

Just brainstorming.

 

[diverdude74]

in the fire service there are bottle similar to what you are talking about. they have a aluminum alloy inner shell, with a total over wrap of carbon fiber, fiberglass and an epoxy resin. These bottles can take pressures up to 4500PSI, but i think the problem with using them for scuba diving is that they would more then likely be extremely positively buoyant

 

[H2O 70]

I do believe that carbon fiber SCUBA tanks rated to 4500psi already exist and are available out there.

 

[Herk_Man]

in the fire service there are bottle similar to what you are talking about. they have a aluminum alloy inner shell, with a total over wrap of carbon fiber, fiberglass and an epoxy resin. These bottles can take pressures up to 4500PSI, but i think the problem with using them for scuba diving is that they would more then likely be extremely positively buoyant

Why would they be more buoyant? Compressed air is not that buoyant, and when the tanks empty, there will be less space inside a smaller tank. I would think the opposite was true. Unless you're just saying that the overall lightness of the tanks would make it more buoyant. In which case I think you'd just have to carry some extra weight. It's an interesting point. Not sure of the physics though.

 

[mfolsom]

I did a google search. This stuff is from 2008. Maybe someone will find more current info.

why dont we have 4500psi tanks? - Scuba Forum - Scuba Diving Forums and Discussion Board

 

[rjack321]

They are made. Yet... The slightest bit of carbon fiber exposed to saltwater sucks bigtime. They have short service lives (15yrs max with 3yr hydro intervals). 6000psi fills are a problem (alot of wear and tear on compressors and regs). Hot fills cooling to less than rated volume would be even more of an issue. Current steel cylinders work fine and are vastly more cost effective for scuba, there's little problem to solve.

 

[Gerbs]

The best way forward seems to be 300 bar (4400psi) steel tanks. Relatively light but with low buoyancy. Commonly available here in Europe. If you partial-pressure blend, you need to be thinking about an (oxygen rated) booster, as otherwise you tend to need more higher pressure tanks for the final top up.

Also, air stops being ideal above 200 bar. At 200 bar you have 195*TankVolume air (use 200, it's close enough). At 300 bar you have 270*TankVolume air (10% discrepancy) . You need to take this into account when planning air consumption and/or partial pressure blending.

If you have a compressor for the fill, then 300bar is the way forward. Total weight per gas carried goes down if you include the required weights.

Gerbs - next rig: double 8L/300 bar. 152 cu.ft or (in real units) 4300L of air...

 

[Rhone Man]

I have always thought that one day we would have coated carbon fibre tanks for diving. Not so much for single dives (because the light carbon fibre tanks are offset by heavier weights), but for expedition diving, it is a lot easier to carry a dozen carbon fibre tanks with one set of weights then a dozen steel tanks and slightly smaller weights.

 

[Blackwood]

I have always thought that one day we would have coated carbon fibre tanks for diving. Not so much for single dives (because the light carbon fibre tanks are offset by heavier weights), but for expedition diving, it is a lot easier to carry a dozen carbon fibre tanks with one set of weights then a dozen steel tanks and slightly smaller weights.

Wrapping metallic cylinders with graphite fiber is one thing, having pure GFRP cylinders is another. Non-destructive testing is outrageously expensive.

 

[Dave1981]

The slightest bit of carbon fiber exposed to saltwater sucks bigtime

Modern performance sail boats usually have carbon rigging and hulls. I don't think it's that much of an issue.

A 6000 or higher fill could be really useful for tec and cave, though with boosters, custom compressors, hoses, fittings, valves, 1st stages and whatnot required I see it being quite cost prohibitive in the short term.