Air cylinders

[Peter69_56]

If you have high levels of oxygen, aluminium is more resilient to the effects of corrosion compared to steel.

When you have lots of tanks, say 2 back tanks and three deco tanks, if they are all steel you will be very over weighted naturally, so if you take some al tanks, when they are used they float thus counter the steel tanks. Each has their good and bad points and no one is right for all situations. For normal recreational single tank diving I would go with steel. If you have a low budget, al might be more affordable.

Second hand tanks can be good value, however remeber you might have to have a hydro done as well as a valve service and that adds to the final cost over a new one which is perfect and has 12 months use until next vis/hydro. A steel tank might have rust and require a clean as well, adding to the cost.

I bought 2 10.5 litre steel doubles for $420, but they needed cleaning and hydro, but were still a great buy over new doubles for $1000

 

[TheHuth]

Well darn, now I'm back to the drawing board. I'm a short light. I guess I'll have to rent a few and see what works best for me.

 

[CuzzA]

That's probably a good idea.

I'm not very tall and don't find the extra weight/bulk of a steel tank any more challenging than an aluminum. The difference is negligible. Any tank is heavy, but once on your back, no problem. Man up.

The caveat is I dive from a boat. If my diving we're going to consists of mostly shore diving then I would consider using aluminum.

 

[Patoux01]

The most general way I can explain the two is...

• Aluminum is cheaper than steel.
• Steel will likely last longer than aluminum.
• Steel is typically heavier than aluminum.
• Steel tanks are usually neutral or negative when empty, whereas most aluminum tanks will be positive requiring excess weight.
• Steel has more options for larger volumes.
• Low pressure steel tanks can be safely overfilled increasing the volume of air.

Mind you, I'll add my view on this... (point by point)

• True
• Maybe, I've had al tanks that were 15 yo, for 200$ a tank, I'm really not gonna cry about 15$ a year.
• Huh? Nawp. Except the short steeel tanks (compacts), aluminium is typically heavier (for same capacity). For same capacity, a steel tank is also smaller.
  
• Yes, they're positive. "Excess weight" however is stupid, it depends on a LOT of factors.
• Yes, that's true.
• "Safely" is a matter of what you believe. I won't overfill my tanks, and know many shops that refuse to overfill them. Get bigger tanks if you want more air, if that's still not enough, get a rebreather.

Let me explain the excessive weight thing. I used about 12# with 2 al tanks in salt water in a 7mm semidry suit. Switching to steel, I had 3# left. Would I keep those steel tanks in fresh water, I'd be overweighted with no weight. People tend to overestimated A LOT the buoyancy of the aluminium tanks...

Many people really like them underwater, their main drawback being that they're so heavy out of the water.

Also, one thing... Aluminium doesn't rust.

 

[CuzzA]

@Patoux01 thanks. If you re-read my post you'll notice I used terms like generally, likely, typically and usually. I did that purposefully because there are a lot of options and configurations that could in specific circumstances contradict my bullet points.

I will concede slightly on my point of tank weight. Perhaps I should have clarified that because most people who use steel tanks do so for the higher capacity of the bigger tanks so the extra weight is something to consider. However, a Catalina AL80 (SP 3300) weighs 31.6# empty with no valve, compared to a Faber 80 (SP 3180+10%) which weighs 32.5#. I chose those two for a oranges to tangerines comparison in service pressure. Now consider this. That AL80 only holds 77.4 cu. ft. of air, however the Steel 80 holds 80 cu. ft., couple that with an overfill and you're now carrying much more weight in compressed air. So the upside to steel is you have a higher capacity of air (a good thing when scuba diving) and your tank will be slightly negative at the end of a dive instead of slightly positive, however the steel tank will be heavier above the surface. Personally, I'll take the steel.

I'll stand behind the rest of my bullet points.

http://www.huronscuba.com/equipment/scubaCylinderSpecification.html

 

[Patoux01]

No idea what a faber 80 is supposed to be....

Luxfer s80: 14.2kg empty
Faber 12.2l: 12.9kg empty
Roth 12l: 12.2kg empty
ECS 12l: 13.5kg empty

Weight of air in each cylinder
(typical s80 is 11.1l, 207b) 11.1*207*1.2 = 2.7kg
(typical 12l tank is 230b) 12*230*1.2 = 3.3kg

full weights:
s80: 16.9kg
faber: 16.2kg
Roth: 15.5kg
ECS: 16.8kg

More gas in the 12l tanks (obviously), less weight when full.


Again, a negative tank is not "an upside". It can be useful, or it can be complete crap.

http://www.eurocylinders.com/Java-Seiten/Tauchsport.html
http://www.xsscuba.com/tank_alum_specs.html
https://www.scubadoctor.com.au/diveshop/index.php?main_page=product_info&products_id=1013


P.S: Are those faber 80 you refer to compact tanks, by any chance?

 

[CuzzA]

To the op, I'll add that if you decide an AL80 is a sufficient sized tank for your diving, then I would stop and consider a Faber Steel 72. They can be found for cheap.

• Actual air volume: AL80 = 77.4, ST72 = 72 @ 3,300 psi and 76.4 @ 3500 psi*
• Weight Empty w/ no valve: AL80 = 31.6#'s, ST72 = 28.7#'s
• Buoyancy Empty: AL80 = +4, ST72 = -3.7
• Size: AL80 = 7.25 diameter & 25.8 ht, ST72 = 6.75 diameter & 20.5 ht.

*Assuming your shop will fill to 3500 psi.

 

[CuzzA]

@Patoux01 we can compare tank specs until we are blue in the face, I'd rather not. In fact I won't. You made a firm point that aluminum is heavier than steel and I showed you "one" situation where that is not true and pointed out my use of general terms. You also claim excess weight is stupid, when we all know a diver should carry weight for the positive lift of a typical AL80 when trying to hold a stop. You mention doubles and we're talking about basic open water single tank diving for a new diver considering buying tanks. For someone reading your post they would draw the conclusion that steel doubles are a terrible idea in freshwater, yet they are used all the time. Which I would agree with except the fact that if you're using doubles you should also have redundant lift from either a backup wing or dry suit.

The bottom line is my general points are accurate. Perhaps we should let the op narrow down his selections and then we can get into specifics.

 

[Patoux01]

Having 2 tanks does not make a dive technical, nor should it be considered "not for open water". If a diver does stupid things "because I have 2 tanks", that's his problem, and he'd be able to get himself in enough trouble with a single tank anyway.

My points were merely to show the OP that there's reasons to dive aluminium tanks, even if you don't like them.

 

[Insta-Gator]

If you are paying attention to your NDL, do you actually gain anything from the extra PSI? More than you need for a single NDL dive, but not enough for a second dive?