Composite Cylinders

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Nick Ruberg

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Scuba Instructor
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South Africa
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Hi,
Is anyone aware of a good manufacturer of composite scuba cylinders. I find lots of threads which are quite old but surely by now in 2016 there should be more manufacturer and I don't seem to find any besides an Austrian crowd.
Any information would be welcome.
 
There are a lot more EU approved, if that helps. But since they pretty much can't be practically used in the US you'll need a European to talk about this.
 
Luxfer as stated above do market a Composite hoop wrapped cylinder of AL 80 size.

I'm not convinced about composite cylinders for a couple of reasons.

From the Luxfer page, A Composite AL 80, weighs 15.3kg its buoyancy when full is -2.2kg and empty +1.4kg

The standard AL 80 weighs 14.3kg its buoyancy when full is -0.8kg and empty +1.9kg

So ignoring the volume difference (approx 30% more) there is little to justify the higher costs and service issues

From a materials standpoint they present a couple of issues

The internal liner is thinner than a standard tank, is is surrounded by a carbon wrap (which prevents the aluminum expanding and allows for higher pressures) this in turn is wrapped in glass fiber as a protective layer

If you get moisture between the aluminum and carbon you get galvanic corrosion - basically it become a battery. This type of corrosion is very aggressive. Because this corrosion is sandwiched between the carbon and aluminum it can't be detected visually. It can be detected by non destructive testing, but they type of inspections required are far more complex than a scuba shop would be capable of. you would need to outsource to a testing house

You can mitigate this with different resins, but there is always a risk. It's hard to tell if the seal that prevents moisture ingress has failed

Manufacturing is more complex because you have to ensure correct saturation of the fibers with resin. too much, you get resin rich areas, too littel you get voids - both affect the structural integrity

Carbon cylinders only have a 15 year life

Thus if more volume is required it is generally cheaper to used steel or bigger aluminum cylinders.

I understand that the military use carbon cylinders - these have a stainless steel liner - but these are for specific uses where the disadvantages are outweighed by operations
 
The tank is toast long before water can wick it's way to the inner liner. Corrosion is hardly worth worrying about. Afterall, that's the point of this style of tank, less corrosion.

The whole tank is coated with a hard epoxy. It's watertight and hard as stone. When that chips, it's pretty obvious. And the fiber wrap will puff out and stretch. A tank like that will kaboom if it's full and you hammer it on rocks a few times. The inner aluminum liner can't withstand 4500psi without the wrap. When they do go up, usually it's a crack that harmlessly vents, not enough force to hurt someone, unless they fall right on top of it.

You'd have to be quite careful with a scuba tank like that, you can't bounce it off rocks like a steel tank. Fire department tanks rarely get much use. The training tank are oftne singled out and replaced often.

These tanks are common in paintball tournaments. It's rare for one to blow up. Noone really tech inspects them.....ever. You just need to keep them "new looking". Usually a thin tack cover similar to a rashy wraps the tank when in use.

PSP2013DallasFriPreview_025.jpg


Painball markers are quite fragile. If they weren't, I'd venture to guess that these fiber wrapped tanks would have never caught on. So the tank, ironically, has an easy life here. Running and sliding into a bunker looks like a guy falling down without wanting to spill his beer.
 
I have heard of a few divers getting killed with these tanks back in the early 80's when they went boom on their backs when diving (my dad was on a dive with a guy when one of the incidents happened) I have also seen what water does to carbon fiber and aluminum, none of it seems to be worth it. if you want light tanks go AL they last longer also.
 
if you want light tanks go AL they last longer also.

For 80's Al is marginally lighter than steel, for 100's steel is marginally lighter than AL. Whats a couple of pounds between friends?


Bob
----------------------------------
...wouldn't use composite tanks on a bet.
 
The only good use I've heard of for these is where you need to carry the tanks long way (multiple miles) cross-country or through horrible areas - like a mile through a 'dry' cave to get to a sump. The weight out of the water does matter a lot there.
 
Evaluate your ability to get a 4350 psi fill before buying. In the US it's nearly impossible, most shops struggle to competently get a 3442 psi tank full.
 
https://www.shearwater.com/products/swift/

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