What is the difference between aluminum, HP steel, and LP steel?

[simmonsjr]

I am planning on purchasing tanks and was just wondering what the difference between aluminum, high pressure steel, and low pressure steel was. I was originally going to go with two AL80, but I've seen several posts saying that steel was a better option. So which way should I go? At this point I am strictly a recreational diver, although I am considering eventually going pro. Thanks for the help.

Jason

 

[Scared Silly]

Get yourself a HP100 ... that will probably last you longer and be more versatile than almost of any other cylinder for general rec diving.

 

[DA Aquamaster]

Aluminum 80s are more or less the recreational standard and they tend to be inexpensive at around $180-200 each - and maybe $100-125 used.

An AL 80 weighs about 33 pounds with the valve and is 4.4 lbs buoyant when empty and it holds 77.4 cu ft at 3000 psi.

In comaprison a special permit steel tank is 2 inches shorter and holds an honest 100 cu ft at 3442 psi, weighs the same 33 pounds with valve but is 1 to 2.5 pounds negative when empty depending on brand, so you can take 5 to 7 pounds of weight off your weightbelt compared to an AL 80. What it measn is that as long as you require at least 5 pounds lead weight, you actually save on total weight and get 23 more cubic feet of usable gas.

LP tanks tend to be heavier as they are made to an older and a bit more conservative standard from older steel alloys. The rated capacity is also a bit misleading as the capacity is at the 10% overfill approved for "+" rated 3AA steel tanks. The normal service pressure for most low pressure steel tanks is 2400 psi and it is 2640 with the 10% overfill. Even that is a bit of a misnomer as the DOT uses rather dated language that considers any tank over 1800 psi as being "high pressure" but it now has little meaning outside the regs.

For most LP tanks of a given size and weight, there is normally a special permit of similar size and weight that will hold a similar volume of gas at a similar pressure. For example a 2400 psi LP 95 is about the the same general size, weight and internal volume as 3442 psi X8-130 and both hold about the same amount of gas gven that the LP 95 will hold 130 cu ft at 3600 psi. That makes LP tanks popular in cave country where you can get 3600 psi overfills in steel tanks, but makes them less attractive everywhere else where an overfill cannot normally be obtained.

LP tanks also tend to be a bit less expensiove than HP steel tanks - approximately $250 to $300 compared to perhaps $350 for an HP steel tank.

These links will help you develop a general idea of how tanks compare to one another.

Scuba specs

XS scuba cylinders

 

[spectrum]

The HP cylinders are a more"elegant package" in terms of getting you light on your feet. This is a big advantage in shore diving and on boat ladders. They do come at a few small costs compared to LP. 1. they cost more, 2. it is a little harder to get a "perfect" fill but not much harder than with an AL80, 3. They may have a shorter lifespan but that's very anecdotal at this point. It is possible that you find yourself someplace that can not take you to 3442 PSI and you need to settle for a short fill. This is usually on boats or a rare land station.

The LP cylinders are heavier. Some of this will be offset by reduced lead but it's not a perfect wash. They are cheaper and easier to fill. They will be longer in length. Especially in the 80 version this can be an advantage for a tall diver as they will trim out nicely. In some locales you can get ludicrous overfills.

The HP 100 is a very nice cylinder. I mainly dive HP80s but either works well with the right weight placement.

If you want to run the numbers this will walk you through it all.

Pete

 

[halocline]

I am planning on purchasing tanks and was just wondering what the difference between aluminum, high pressure steel, and low pressure steel was. I was originally going to go with two AL80, but I've seen several posts saying that steel was a better option. So which way should I go? At this point I am strictly a recreational diver, although I am considering eventually going pro. Thanks for the help.

Jason

I think it will pay off for you to try a few different tanks before you buy. As a few others have said, the HP100 is a very versatile tank, but you should consider what you will need at your height/weight for the local sites you will be diving. Try to connect with some experienced local divers and talk to them.

As an example, the local diving I do is usually in 20 feet of water, rarely in more than a 3mil suit, and I usually use a LP72 steel or AL80, preferably the 72. At the one ocean site I drive to, the Flower Gardens, I like having more air for the deep dives so I bought a HP100.

If you post your height, how much weight you usually use, and what kind of diving you'll be doing locally, and you might get some good specific advice about what tank could be ideal for that. I

 

[simmonsjr]

If you post your height, how much weight you usually use, and what kind of diving you'll be doing locally, and you might get some good specific advice about what tank could be ideal for that. I

I'm 6'3" and will be doing mostly reservoir diving for the near future. As for weighting, I'm in the process of replacing my gear right now as it was all stolen a while back so I don't yet know what I'll be needing with the new set up, but I was a tad heavy with the old one.

If it matters I am also considering taking GUE Fundamentals down the road as well.
Thanks

 

[imwright1985]

al tanks are cheap and very easily attainable, hp steel is better for smaller size gear and the bouyancy characteristics allowing you to lose weights, and lp steel are very conservative but bigger dimensions with similar bouyance factor as HP steel. Aluminum tanks have thicker wall dimensions which allow more displacement of the material for cyclidic loading (filling and draining) which depending on the actual alloying of the material can add longer service life aluminum oxidizes slowly compared to steel and doesnt have as much of a tendancy to grow through the material like steel, which allows you to catch it and keep the outside of the tanks cleaner easier to prevent excessive ware/errosion. also remember that 1988 and older al tanks are being refused fills at various shops because some had bad alloying characteristics and like 6 or 7 of them blew up. Around here AL80 is about 150, HP100 is about 250, and i dont know the price of the LP steels. Hopefully with this and how badly you will abuse your tanks you can figure out what you want.

because of cost and the fact the tanks are usually abused you see almost all rentals are AL

 

[TSandM]

If you are planning on diving a stainless steel backplate in relatively shallow fresh water, you might be fine with an Al80, and they're cheap. You can also use them as stages later on (or double them up for fresh water diving).

 

[ShakaZulu]

There are also buoyancy issues to be aware off....generally, the HP100's are nice tanks. Are you diving warm/cold water?

 

[halocline]

I'm 6'3" and will be doing mostly reservoir diving for the near future. As for weighting, I'm in the process of replacing my gear right now as it was all stolen a while back so I don't yet know what I'll be needing with the new set up, but I was a tad heavy with the old one.

If it matters I am also considering taking GUE Fundamentals down the road as well.
Thanks

The amount of weight you anticipate using will be important in the decision for a tank. Since you're taking the GUE route, you'll be in a backplate, probably steel, and maybe a drysuit? If you're in a drysuit then almost certainly you'll benefit from the buoyancy of a steel tank, but if you're in a relatively thin wetsuit then the AL80 might work well. Once you figure out the weight/exposure suit situation, start looking for deals in your area. Used tanks are the way to go IMO. Also, if you're heading in the tech direction, you might also think about buying tanks that will make good doubles. Someone was recently selling LP85 doubles in the classified forum at what looked to be a good price. Those would be my doubles of choice, but I'm a lot smaller than you are.

If you can find some galvanized LP72s in your area I would always recommend buying them, because to me they're great for shallow dives and they can cost almost nothing, plus they make good starter doubles. You should be able to find them for under $50 plus hydro (another $20 or so) If you doubled those you could even switch the 7" bands and manifold over to LP85s later on if you need more gas and/or you can find a deal on some.

I'm not suggesting that you start diving with doubles right away, but if you're going to take tech diving classes, chances are you'll end up in doubles eventually. It makes sense to buy tanks that you can use down the road as well.