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#829
Steel vs. Aluminum Tanks
k-lambertus - 8/31/2011 10:58 PM
Category: Equipment
Replies: 25

I have two 80 cu. Alumn tanks I like them but I recently went diving at the Outer Banks and the dive operation used Steel which I fell in love with. The thing was is they my tanks had over 3700 psi so with my nitrox mix at 29 percent I actually ran out of PO2 before I ran out of air. I returned to the boat with over 600 psi every dive. I since have ordered 2 Steel 85’s from my instructor which I should be getting this week. My one buddy said I was crazey because everyone I dive with uses Alumn 80’s and why should I go and get 2 Steel 85’s. Since completed my rescue course I feel more comfortable having more or different equipment i.e. My buddy carries a dive knife I carry dive shears incase I need to remove a wetsuit in an emergency. So back to the tanks, I feel having more air 85 cu steel with 3600 psi if there is an emergency I can buddy breathe with him even to do a safety stop where as if I had an alumn 80 with 3000psi if he for some reason ran out of air near the end of the dive I would likely not have enough air for both of us to do a safety stop. Maybe I am thinking into it to much but I see no reason why having more air than everyone else I dive with is a problem.
#4553
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scubaman - 8/31/2011 11:50 PM
How much for the 80’s.
#829
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k-lambertus - 9/01/2011 5:47 AM
I am still not sure if I want to sell them yet but i will let you know if I do.
#4553
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scubaman - 9/01/2011 6:33 AM
Sounds good, if you decide to sell, give all the info. you would expect to get before buying. i.e. how long have you had them, etc.

Dudley
#5727
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johng - 9/01/2011 9:01 AM
Do the shops in PA have any problems overfilling steel tanks?

In North Florida they do but they dont down here where I live.

Are you looking at high or low pressure tanks?
#829
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k-lambertus - 9/01/2011 1:23 PM
I am gettting low pressure tanks. My instructor does alot of cave and tech diving. He ordered me 2 tanks when he ordered himself 2 tanks for sidemounts. Yes I can get them stuffed with 3600 psi you just need to know who to talk to. My instructor says all the tech divers overfill. 
#1321
midas6t6 - 9/01/2011 6:29 PM
The steel 85s will only give you 5 cu ft more air than the aluminum 80s if both tanks are filled to their rated limit so no real issues as far as diving together regarding length of the dive. Some of the advantages steel offers are longevity (if cared for properly), you’ll have to carry less weight to adjust your buoyancy (partially replaced by the weight of the tank) and smaller size relative to an aluminum tank. If you haven’t bought yet, check into getting 100s. They’ll give you the extra capacity should you need to buddy breathe will someone on an 80.
#1321
midas6t6 - 9/01/2011 6:32 PM
I’d also recommend getting hi pressure tanks for the size advantage vs a low pressure of the same capacity.
#5727
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johng - 9/01/2011 7:22 PM
a Lp 85 and an Hp 100 are pretty much the same tank when they are filled to 3600 psi.
#5727
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johng - 9/04/2011 7:59 PM
From EskimoBluDay:
From midas6t6: The steel 85s will only give you 5 cu ft more air than the aluminum 80s if both tanks are filled to their rated limit

Just to be a PITA (actually someone once corrected me on this) the AL-80 only holds 77 CF so the difference is 8 CF - not that it really makes much difference. LOL

Actually if you read the original question you would have realised we are talking about more like a 35 cu ft difference.
#1321
midas6t6 - 9/05/2011 6:53 AM
original post was steel 85s vs his buddies alum 80s - that’s 5 - 8 cu ft, where does 35 come from??
#5727
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johng - 9/05/2011 8:26 AM
A low pressure 85 with a hydro + stamp has 85 cu ft at 2640 psi.

When you put 3600 psi the tank will hold 115.9 cu ft.
#1321
midas6t6 - 9/05/2011 7:40 PM
Manufacturers make hi and low pressure tanks for a reason. Buy a tank with the capacity you want at it’s rated pressure. Overfilling will void any warranty and lead to premature failure at best, it could be a bigger problem should it fail at depth.
#1292
Horizontaldiversllc - 9/05/2011 9:07 PM
i use a 130cf steal tank when spearfishing and my girlfriend uses a al80 our air consumption matches pretty close she sometimes buddy breathes on the safety stop
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johng - 9/05/2011 9:58 PM
From midas6t6: Manufacturers make hi and low pressure tanks for a reason. Buy a tank with the capacity you want at it’s rated pressure. Overfilling will void any warranty and lead to premature failure at best, it could be a bigger problem should it fail at depth.

The low pressure tanks are the tanks of choice for a lot of technical divers for a variety of reasons. Size, length, how they trim out. The fact that you can get more gas in a smaller package....

did you ever think hes not over 6 ft tall and doesnt want to be foot heavy with bigger tanks?

How does a tank fail at depth With pressure surrounding it?
#1321
midas6t6 - 9/06/2011 8:06 PM
These links will give you a better idea of the specs and buoyancy characteristics of HP and LP steel tanks. A HP100 is 9 lbs lighter than a LP95, same length, virtually the same buoyancy characteristics:

http://www.xsscuba.com/tank_steel_specs.html
http://www.divegearexpress.com/library/tanks.shtml#dimensions

Chronically overfilled tanks fail from metal fatigue, a gradual weakening of the metal from stress. The farther over a tanks’ rated fill pressure the more stress on it.
The pressure on a tank underwater is insignificant compared to the pressure from within the tank - 1 atmosphere = 14.7 PSI - you’d have to go pretty deep to equal 3600 PSI, so the water pressure is not going to prevent a tank from failing.
There is some inherent risk while diving which we all accept, otherwise we’d be playing croquet. Why add an unnecessary factor?
#5727
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johng - 9/06/2011 9:47 PM
From midas6t6: These links will give you a better idea of the specs and buoyancy characteristics of HP and LP steel tanks. A HP100 is 9 lbs lighter than a LP95, same length, virtually the same buoyancy characteristics:

xsscuba.com/tank_steel_specs.html
divegearexpress.com/library/tanks.shtml#dimensions

Chronically overfilled tanks fail from metal fatigue, a gradual weakening of the metal from stress. The farther over a tanks’ rated fill pressure the more stress on it.
The pressure on a tank underwater is insignificant compared to the pressure from within the tank - 1 atmosphere = 14.7 PSI - you’d have to go pretty deep to equal 3600 PSI, so the water pressure is not going to prevent a tank from failing.
There is some inherent risk while diving which we all accept, otherwise we’d be playing croquet. Why add an unnecessary factor?

Are you trying to start an argument here???

From the comments you are spitting out I know you have never dove a steel tank. I would go as far to say youve never dove anything past an al 80.

You threw in that lp 95 to force an argument. First of all you are missing a ton of facts. A lp 85 is what you compare to a hp 100 not a lp 95.

The lp 95 you described is a Faber Tank and you compared it to a hp 100 Worthington. Worthingtons are more negative then Fabers so your fact is flawed from the start.. Fabers are less negative then worthingtons...

Faber makes Hp 100s and lp 85s but Im not going to bother looking up that crap because you will for me to find out you are wrong... You knew that and threw in the 95 argument to throw people off.

Nevermind I did look it up a Hp 100= -14.11 an Lp 85 = -3.80

(Oh! XS SCUBA tanks are Worthingtons)

NUFF said!!!
#829
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k-lambertus - 9/06/2011 9:57 PM
WOW I really didnt mean to stir up a hornets nest with this one. Sorry everyone.
#5727
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johng - 9/06/2011 10:09 PM
From k-lambertus: WOW I really didnt mean to stir up a hornets nest with this one. Sorry everyone.

You asked a fair question. and got a fair answer.

I dive lp 85s I have 4 for sidemount. and wouldnt dive anyhing else.

When you talk to your instructor ask him to let you try them some more.

Im sure you will like them. the other guy is making statements for the sake of an argument... hes never dove a steel tank and cant prove he has....
#1321
midas6t6 - 9/07/2011 6:07 AM
I dive with Faber HP117 steel tanks, I also have aluminum also. The LP95 was compared to a HP100 just to give a comparison of similar capacity tanks. I was not trying to start an argument, just promote safe practices and present data thru the links to make accurate comparisons.
#310
jnowak100 - 9/24/2011 8:25 PM
There is a lot to be said for more air, I have recently started using steel 120’s instead of AL 80, you can drop a lot of weight, you have a lot more air, You will more like run out of ND time before your air.
#315
pmombourquette - 12/25/2011 7:25 AM
I dive Worthington 120’s , on dive over 100ft, lend my buddies my extra 120. That why you should always get tanks in pairs. I also take 10lb off my weight belt, which is a big deal when diving 40 deg water. The extra air is great when diving with inxperianced divers too. I don’t worry about draining my tank with someone attached to my octo on a 100ft dive.
#2231
MDW - 1/04/2012 4:40 PM
I have traditionally (for the past 10 years) preferred LP steels for the following reasons:
1) I need no weight belt (single 120, double 108s, even single or double 72s)
2) I don’t pay 50% extra for the HP fill ($9 vs $6 for LP fill)
3) I have as much or more air than with AL80, even at LP (much more with overfill)
4) A slight overfill (3000psi) is still a cheaper LP fill
5) Long life of tank (I have several Steel 72s from the early 1970s, and they all easily pass hydro every time)
6) Cheap to buy used - I’ve bought all mine used for $50 for a 72 to $150 for a 120. I just don’t trust a used AL80 to not have been abused.

However, lately I have branched out to a wider variety of tanks for different uses:
1) Double AL80s for warm water in a wetsuit
2) Double HP80s (from the 1990s) for their short height, small diameter, and medium weight
3) Double steel 72s a really cheap set of doubles, smaller & less buoyant than AL80s
4) Double LP108s for cold water in drysuit and those long deep dives
5) Two AL50s side mounted under arms (for shallow diving in wet suit) Very maneuverable.
6) Two steel 72s side mounted for longer or deeper dives still with excellent maneuverability.
7) Single AL80 or single AL30. These are really only good as stage or deco bottles along with one of the primary setups above.
8) Single LP120 with Y valve for medium dives in cold water with dry suit. Y valve allows use of doubles regulator setup on this single tank. Same buoyancy characteristics as the double LP108s with less total weight and less total volume.

I was a little hesitant about the HP80s, but for $150 including 2 tanks, manifold, & bands, I couldn’t pass it up. We’ll see how I like paying $18 for 160 cu ft of air when I’m used to getting 216 cu ft or more for $12 in the LP108s. The HP80s are really comfortable to wear, though because they are so short and skinny.

My recommendation to anyone is to find some nice old steel 72s and buy a half dozen or so for the cost of one new HP steel tank or 2 AL80s. Then you have enough of them to make 2 sets of doubles or 2 side mount setups plus a stage and a deco bottle or 2 single tank setups. I’ve found that just a slight overfill of these (to about 2500psi in the 2250psi-rated tank) gives you as much air as an AL80 at 3000psi in a smaller package with better buoyancy characteristics.

Mark
#446
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BoxsterMan - 2/14/2012 3:36 PM
To each his own. Just remember that overfilling tanks stress the burst discs, so they should be inspected from time to time. I doubt that the hydro guys even bother to look at hydro time.

Also, consider the forces that the threads have to contend with when overfilling. I’d make sure the VIPs are done at a reliable inspection station, rather than some newbie instructor at a dive shop where staff come and go a lot.

Consider that an 80 cuft tank @ 3000psi has about 1,000,000 lb of potential energy stored, and it’s on you back or under your arms...

But, regardless of your choices, dive safe! Cheers!