US cylinders,sizes,pressures?

[Rick Murchison]

Weight wise aluminium cylinders are heavier on land than their steel counterparts (or should be) due to the thicker walls required.

Maybe its regional as steel tanks are cheaper than Al. here - the only real use for Al tanks here tend to be as stages. That said im looking right at a 7l steel O2 stage at the moment

Here, money's the real difference. For most folks who've tried them, steel cylinders and their buoyancy characteristics get "love at first dive" reviews. When I was a youngster I could dive a steel 72 with no BC, no wetsuit and no weightbelt and be neutral in the ocean. My AL80 equipped buddies had to carry weight. (Now that I've cultivated a respectable table muscle , I can dive that way in the lake, but need 6 pounds in the ocean.)
I do prefer AL for stages and deco bottles, but for all back gas cylinders I prefer steel.
Rick

 

[spectrum]

My take on aluminum tanks' popularity:

1) Aluminum is far less expensive.

Mainly if you go for items in short supply. I just bought two Pressed Steel E7-80 for $205 each, more than aluminums to be sure but not as painful as the e7-110s going for $330.+ The steel tank does not short sheet you like the AL80 that really fills out around 77.4 CF.

My take on aluminum tanks' popularity:
2) Aluminum is lighter in weight.

Since I don't have wear lead to keep it down for my stop with an E7-80 and even empty it contributes some negative buoyancy I drop about 7 pounds from my belt. The tank is also lighter than a standard AL80 making me 10 pounds lighter overall as I walk to the water.

3) I think aluminum tanks are slightly positive in buoyancy when empty, which I'm not sure is a good thing or bad, but is something to consider.

You are correct on standard cylinders. IMO it's undesirable for a cold water singles diver. Can be an asset for a cold water doubles diver and is a minor issue for a warm water diver since the little added ballast they need to wear is added to a light load to begin with.

4) Aluminum doesn't rust, although I understand it does oxidize in another form.

And that can be in the form of a dust that you can end up breathing in. The actual effects are controversial but cannot be good. Rust is generally too coarse to make it into your delivery system.

(Incidentally, I am aware of the difference in spelling for this material between US and UK. Quite interesting, I think, although inconsequential for this conversation. )

I never noticed the spelling. I thought everyone on the Discovery Channel just pronounced it differently.

I read somewhere that AL80s in particular are so common because they represent an "optimal" compromise between air capacity, strength, and cost.

I would add to that statement: Since the indusrty is driven by the warm water resort diving industry where heavy exposure protection is not the norm.

I would underscore cost.

I'm not so sure about leaving the word strength in there. It works but needs to be watched and has a considerably shorter working life in terms of cycles.

I personally own an AL90, btw.

cheers

Billy S.

If it works for your diving and it's paid for then it's a great tank. This is one of those topics where the best answer is colored by what and where. I think it's becoming fairly accepted (I'm sticking my neck out here) that steel is superior BUT in the right application aluminum can be a fine alternative and if thats what you can afford it beats sitting on the beach.

Just my opinions and understandings for what they are worth.

Pete

 

[chaz]

I was told that Steel and aluminum oxidize differently.
That Steel rusts along the surface, which can be corrected without significant loss of quality.
But Aluminum oxididation forms pits that quickly sink into the metal. Once an AL tank starts to oxidize it's life expectancy is very short.


Can anyone confirm this?

 

[Charlie99]

I was told that Steel and aluminum oxidize differently.
That Steel rusts along the surface, which can be corrected without significant loss of quality.
But Aluminum oxididation forms pits that quickly sink into the metal. Once an AL tank starts to oxidize it's life expectancy is very short.


Can anyone confirm this?

I don't know about tanks specifically, but the reason that steel "rusts" while aluminum doesn't is that iron oxide tends expand, then flake off and expose new iron to oxidize; while aluminum oxide tends adhere and form a skin that resists further oxidation.

 

[ChrisA]

Aha as simple as that Was expecting some other technical reason.

First, AL tanks cost less. But which is more common depends on where you dive and the water temperature. Here in California we have colder water and thicker exposure suits and so need more weight. May as well use a heavy steel tank. However in warm water as in Florida you would have very little ditchable weight if your tank as 8 pounds negative.

It is not unxommon to find divers here diving metric, making three meter safty stops and using
gages marked in bars. Don't worry. Do it your way and no one will complain. Just make sure your buddy understands bars and you psi.

 

[dlegros]

I would hazard a guess that aluminium is cheaper in the US as a lot of the stuff comes from the states.

I don't think we have vast reserves of aluminium ore (bauxite isn't it?) in the UK.

Dom

 

[Kim]

In Japan steel and aluminium tanks are about the same price. I've never seen anyone dive aluminium here although I suppose probably the techies in Tokyo use them.