Aluminum Doubles??

[JahJahwarrior]

It just gets old trying to refer to each tank by (adjective)+pressure.

You have:
old low pressure 2250, new low pressure 2400, new low pressure with overfill to 2640, normal pressure of 3000, then of course the 3300 psi aluminums, then the E/X exemption tanks, modern high pressure at 3442, and true high pressure at 3500, and don't forget the freaking high pressure 4500 carbon fiber wrapped tanks.

When talking about strictly aluminum tanks, some call the 3300psi tanks "high pressure," whereas most would call them "mid pressure." Nowadays, we call the 3442psi tanks "high pressure" but that's not really true high pressure, which is 3500psi. So some people call the modern high pressure tanks "mid pressure" but then you need "mid pressure 1" and "mid pressure 2" to distinguish between 3442 steels and 3300 aluminums.

Then you get the arguments about LP and HP tanks being the same metal, and about the safety of 6351 alloy aluminum cylinders, and no one can agree on a proper cave fill pressure, and tanks, which should be the simplest scuba device (it's a giant piece of metal with no moving parts...), become one of the most complicated things.

[Diverlee]

You don't see many double 80s in FL anymore, but there isn't a problem, except they don't hold as much gas, and require weight to use with a dry suit.

I used them for several years. They were all I had and also all I could afford. If I remember I used 15# of wt when diving dry in fresh and 26# in salt water.
When I had some extra money I changed to LP 85's which I still use today and love.

[scoupland]

I dove AL 80 doubles in Mexico. That was all they dove there. I saw a few steel tanks but they were novelties. In FL I sidemount with steel 133s (3442 psi). Big tanks I know, but I am 6'7", 260lbs so they are no problem for my size. When I purchased them from Diver's Direct they were sold to me as "high pressure" tanks. Whatever they are called, they can hold a lot of air.

[Gary]

Low Pressure tanks were always a bad idea. Some people claimed that low pressure was easier on the regulator HP seats - which would be true if they didn't then over-pressurize the tanks anyway.

The only real reason people got the LP tanks was because they were big and held a lot of air when you over-pressurize them.

Now almost all the LP tanks have a HP equivalent.

There are still some LP tanks that still have some reasons to use. Many of the Faber tanks and the LP 85s and LP 120s have better buoyancy characteristics in the water which is especially important when sidemounting. Also the LP 120s were not re-designed and re-rated for higher pressure and are still only available in the LP version. (There are few people who dive them because of their huge size and weight and probably weren't considered worth the cost of re-rating them for the number of people that would buy them.)

[MedCop]

I have a set of AL80 doubles that I recently put together as I got a good deal on bands and manifold..yet to dive them. Will most likely take them apart and use the 80's as stages or sidemount in open water.

I did dive AL80 doubles in the DR as that was all that was available...and it was shallow.

[FW]

HP vs LP

A much better way to judge tanks is by internal volume. In Europe, tanks are designated 7 liters, 10 liters, etc. It is much easier to tell how much gas they will hold. The big problem with "HP" tanks is the wall thickness. In the past, HP tanks had thicker walls to allow them to be called HP. This reduced the internal volume, and made them heavier.

The bottom line - an HP120 holds 120 cu ft at about 3500psi. A LP120 holds about 170 cu ft at 3500psi, and is lighter in the water. My numbers may be off a little, it is too early in the am, but this gives you a good idea anyway.

[jpdiver]

Peter, HP cylinders are no longer being sold. The "HP" designation refers to a particular model, one feature being the tiny neck. The "higher pressure" cylinder is correctly refered to an E-Series or X-Series, depending on the manufacturer.

When people confuse these with "HP" cylinders it's a sure sign they haven't been in this sport too long.

wrong! People referring to the E series 100 and 120 cu ft tanks as high pressure tanks have probably been in the sport a long time not a short time. The Genesis HP 120's have been the staple of Northeast Wreck divers for years and years. They are rated at 120 cu ft at 3500 psi. Low pressure tanks such as the Faber 104's, are 104cu ft at 2640 PSI and of course hold more on a "good fill". Shops in the Northeast will not fill these beyond 2640 so the HP 120's are the standard. The Genesis 120's are 7.25" diameter while the 104's are 8"

Now that the Genesis 120's are no longer available, it is easy to see why the newer pressed steel "E" series 120's could be referred to as High pressure. They are also 7.25" diameter with a fill pressure of 3442 (a small difference from 3500) and much greater than 2640.

Yes the E series do use a 3/4 inch valve thread vs the 7/8 thread of the older Genesis. The 7/8 is actually a smaller diameter thread than the 3/4. The 7/8 is a measure of length.

So- if a diver refers to such tanks as high pressure, I would not infer they are inexperienced. They could have 20 years or more diving wrecks such as the Doria, U869 etc.

[Sludge]

I'm famous for splitting hairs. Referring to the E-Series as high pressure is technically correct. By definition, all scuba cylinders are high pressure.

It's referring to them as HP where I have an issue. HP cylinders have the skinny neck.

But as a friend of mine is wont to say, "A hundred years from now nobody will care."

[paul19may]

Why do you guys prefer Lp over Hp can anyone truly explain the difference. I see all the time that the folks on here are diving LP's. Just curious hopefully this isn't a stupid question. I'm asking because Iam curently looking for my first set of doubles and need reccomendations from the experienced....

Given the general direction of the question, a little example might help: for the sake of argument let's define LP= 2400 PSI and HP= 3000 psi as these serve for the purpose of illustration (I know that the definitions vary- but bear with me as I am a Brit and am limited to understanding things measured in litres and bars).

So a LP98 will hold 98 cu ft gas at 2400 psi, or by overpressuring the tank to 3000 psi, you can get 120 cu ft gas (3000 * 98/ 2400).
Whereas the HP98 at 3000 psi will give you only 98 cu ft.
ta da! More gas for the same (high) pressure, although the LP and HP cylinders may be physically slightly different in size, they are both rated as holding the same gas volume when filled to their specified pressures.

The details and definitions may differ but the general idea is there.
Hope that helps and was not redundant.

Of course, even the high pressure of 3442 psi (237 bar) is considered weedy by we Brits where hp= 300 bar. No wonder we owned the globe, had an empire and to bastardise and misquote a Prairie Home Companion, Britain- where all the men are strong, all the women good looking and thechildren are above average!

Flame at will.

Best P

[J_glenn06]

So if I was to Dive alm doubles no one would look at me and be like Haha wow look at that Guy what a loser!!