Carbon Fiber Tanks

[DA Aquamaster]

That is nice but we still live and dive in the real world and carbon fiber 4500 psi tanks will require a change in infastructure to support them to full advantage. Then there is the durability issue.

In the real world, I can normally get 3500 psi in my HP steel tanks from most shops (but not everyone can) but 3500 psi can be hard to get on many dive boats. I can also get 3600 psi in my 2400 psi tanks in N FL and about 3000 psi in them in NC, so underfills are not a problem with 2400 or 3500 psi tanks but would be an issue in many more places for the forseeable future at 4500 psi.

I do not have to worry about pushing either steel or aluminum tanks through a wreck or restriction in a cave and I do not have to worry about the tank banging against the rail in 6 ft seas as both materials are quite gouge resistant - steel much more so than aluminum. Steel tanks will last 50 plus years and aluminum tanks hold up well even after 25-30 years. Hoop wrapped CF tanks are currently limited to 15 years of service life in the US and many require hydro tests every 3 years rather than 5 years.

Externally, a CF tank is very prone to damage and any damage of the carbon wrap or pentration of water to the carbon fiber wrap will condmen the tank. Internally, the aluminum in most hoop wrapped SCBA tanks is much thinner and consequently any pitting or corrosion internally is much more vital and the tank will be condemed with a much smaller pit than is the case with a normal AL tank. They are in short, not all that ammenable to use in water.

Personally, I think they will have lightweight pretty fish diving recreational applications long before they have technical diving applications just due to the damage that would occur to CF tanks in wreck and cave penetration.

 

[Rhone Man]

I agree with all of that, although I suspect it would not take much to make them rugged enough for tec diving - any rigid shell would not expand sufficiently, but presumably they could get a rubberised coating.

 

[WD8CDH]

There is a maximum usable pressure for SCUBA tanks for any given material and that is the point where the tank has excessive negative buoyancy.

For the steel used in 3AA tanks, that is about 3000-3500psi. Beyond that, except in small tanks like my AGA 4400psi (4000 +10%) tanks, they become too negative to dive with.

For the stronger steel, like what is used in SP or Exemption tanks, it is about 4000psi when the walls become too thick for practical buoyancy characteristics.

For 3AL tanks, it is about 3500psi.

Titanium in the right alloy could go up to an impractical 10,000psi but the cost would be prohibitive in any alloy due to manufacturing difficulties.

The interesting material is 7000 series aluminum. You could go with a wall thickness that would have a service pressure of over 6,000psi before the tank would be too negative for diving. This material is currently in use for cylinders in other markets and has a proven track record at 300bar and is not much more expensive than 6061-T6 alloy.

At 4500psi, you could have a tank with all of the advantages of a 4500psi Carbon Fiber tank without the disadvantages of cost, delamination and be more gouge resistant.

Eventually, I think 300 bar or 4500 psi will be just as common in the US as it is now in Europe.

 

[crpntr133]

I agree with all of that, although I suspect it would not take much to make them rugged enough for tec diving - any rigid shell would not expand sufficiently, but presumably they could get a rubberised coating.

Rubberized coatings were tried many years ago and it was found to trap water and hid any problems from vizual inspectors. Personally I don't see these tanks taking off.

 

[WD8CDH]

A shell is a much better choice for tank protection. By the way, the CF tanks are much more rugged than most divers think. Firefighters really abuse their tanks and still very few are condemed. In the US, there are now 30 year CF tanks and in Europe, there are unlimited life CF tanks.

 

[WD8CDH]

Well, I just got a shock today. I just looked at the SCUBA section in the Luxfer website and they only list the Aluminum 40, Aluminum 80
and the Carbon Fiber 106????????

http://www.luxfercylinders.com/products/scuba/specifications/us_imperial.shtml

 

[ScubaSteve]

Diving these tanks with the tank set weighted neutral is very comfortable due to less bulk and better trim than conventional systems.

This to me seems like a misleading statement because the same trim can be achieved with any tank. Trim is simply the divers placement in the water column and the resistance they are faced with because of their placement. The more streamlined they are (themselves and their equipment) and the more horizontal they are in the water, then the better the trim. You can diver perfectly horizontal with an AL80 or a STL 120 or any tank as long as your weight is spread out properly. The tank only has to do with what weight you carry and where it gets put to trim a diver (i.e. more weight carried for an AL tank than STL).

 

[WD8CDH]

Hi Steve,

Good points.

I consider trim both fore/aft and if the tanks are pushing down on me or trying to lift me up by the straps. So, I look at adding weight to the tank set vs. to the diver as part of the trim too.

If the tanks are negative, you can't trim them to be not negative by adding weight. Of course, if the tank set is not excessivly negative, it's not a problem but there are some very negative tanks that will tend to make the diver turn turtle even if the fore/aft trim is correct.

 

[JonW*Interspiro]

Hi Guys...I hope you don't mind if I chime in here. This is Jon the Interspiro Rep for the Southeast and I hope I can shed some light on the topic. First, our carbon fiber cylinders are 4350 psi and are US Navy and DOT approved for the US markets. They are fully composite and significantly liter than aluminum or steel cylinders. Our 72 cubic foot weighs just 21 lbs full of air. The brass weight is a quick attachment to produce neutral buoyancy. This greatly reduces the weight on a divers back at the surface until he is ready to dive. Very little additional weight is needed for negative buoyancy and the added weight necessary depends on the suit the diver is using and his body composition. The 140 cubic foot cylinder weighs about 38 lbs full...still much lighter than an 80 cubic full plus almost twice the air. In Europe, these cylinders have an indefinite shelf life as long as they pass hydro. Here in the US, thanks to the DOT, we have a 15 year shelf life, every 5 year hydro and internal visual and a yearly external inspection.

Is our system for everyone? Probably not. It is not as cheap as some of the other equipment on the market, but if you like to have a quality system that is dependable with high performance, it probably doesn't cost much more than the equipment you are currently diving. We use time tested components that require very little maintenance which equals reliability like our MKII mask commonly known as the AGA mask. I have seen other posts in the forum about the Guardian mask and the responses. The concern I would have is the reliability over the long run as compared to the AGA. key is always proper maintenance and care for any piece of equipment.

I doubt I answered all the questions, but feel free to contact me if there is anything can be helpful with. And better yet, if you would like to see any of our products up close, we can arrange a regional demo in your area if you would like to be the sponsor. Sponsoring earns a discount on any equipment purchase.

 

[Indian Valley Scuba]

We actually have the cylinders here in our shop that you saw at Beneath the Sea. We have them set up as doubles, with a full face mask system.

We are playing with the counterweighting to achieve neutral buoyancy in various waters.