Why Aluminum ?

[elan]

I was watching some USD catalogs yesterday and noticed that Aluminums started appearing at the end of 70th. Given the existence of LP72 at that time what was the selling point for those tanks, LP72 seems to be a better tank overall.

Can anyone who witnessed the appearance of those tanks give some details ?

 

[Eric Sedletzky]

They were cheap and held a little more air. Good for the budding exotic tropical dive operations of the time.

 

[Luis H]

In 1971 the first aluminum tanks showed up in the US. They were introduced by US Divers. They were Special Permit tanks with 72 cu ft capacity and were stamped 2475 psi. They were 6.9 inches in diameter (the same as a steel 72), but much taller. They were 9 lb positive when empty (they were called floaters, buoy, etc.)

It was also advertised as not having a need for getting it + stamped in the future.

Most divers with these buoyant tanks would add a steel 72 boot (rounded bottom tank boot on a square bottom tank) and used the space inside the boot to add some lead. It made the tank that much longer (and heavier), but at least the buoyancy was manageable.

The original aluminum tanks were awful, but they were advertised as rust proof (corrosion resistance). Corrosion on steel tanks was a big issue. Yearly internal inspections were introduced for the same reason.

I almost bought one of those aluminum tanks as my first tank. I am so glad I didn’t. They were advertised as a great improvement and with a great introductory price (the steel tanks was still less expensive).

The original aluminum 72 was soon replaced with 3000 psi tanks. In particular the US Divers aluminum “80 Professional” caught on quickly for its extra air. The newer 3000 psi tanks were not as buoyant… they were actually a big improvement.

Again the corrosion resistance was the original big seller. Aluminum tanks were originally more expensive than steel 72.

In the Caribbean were large fleets of rental tanks get a lot of abuse with minimal internal tank inspection the aluminum 80 does make sense, especially since it is less expensive for the dive operators.


Added:
I love my steel 72 (I have about 12 of them) and my other steel tanks, but my favorite tank is a rental aluminum 80 down in the Caribbean.

 

[elmer fudd]

Where I live aluminum tanks are a tough sell. They're way too buoyant, have a small capacity and are nearly the same size as HP120's. I understand that in the tropics though they like that near neutral buoyancy. I've heard that tech divers often like that too for stage and decompression bottles. Because the tanks are nearly neutral it doesn't affect your weighting much if you pick one up or leave it behind. Pick up a full HP119 and you're suddenly 10 lbs more negative.

Pony bottles here are generally aluminum too and for the same reason.

 

[elan]

Thanks, gentlemen for the history. Its always nice to hear the story from someone who saw it with their own eyes.

 

[elan]

Elmer I know the pros and cons of mordern aluminum tanks, the question was more about their place in that period of time.

 

[danvolker]

Elmer I know the pros and cons of mordern aluminum tanks, the question was more about their place in that period of time.

As Luis said, rust in your tank was the big factor that lead most divers I knew in the 70;s and early 80's, to switch to Aluminum.
Many of us however, preferred the steel 72's.. I know I did....I used them on through the mid nineties, and had several sets of double 72's --they made very well ballanced doubles setups, and I would usually fill them hot for tech dives, closer to 3000 psi ( making them more like 80's for volume). When my 72's started failing hydro's, it became time to move to theAL 80's....

And now, all over again, the AL 80 is a LAME tank.
Most divers in Florida dive Nitrox today, and for 80 and 100 foot deep dives with Nitrox, the 80 al is a crappy choice....While it was fine for air durations, for Nitrox on these very standard dives, the far better solution now will be hp100 steels.... ( and no one is worrying about rust)..... In all fairness to the old steel 72's, I ran mine into the mid nineties, with huge use, and there was never a rust problem.....I think this rust issue stemmed from the frequent practice of the era, to wait for your last breath, pull the j valve, shoot one more fish or grab one more bug, then free ascend with an empty tank....Many people back in the 70's would ALWAYS stay down till the tank was empty--that is what signalled the end of the dive..salt water could enter the tank...and this was bad for the steel 72's

 

[elan]

Thanks that explains a lot. Interesting indeed!

 

[captain]

Compressors back in the day didn't have the filter systems of today's compressors. The US Divers compressor I bought in 1968 only used only charcoal in the filter, no type of desicant was used before the charcoal like today. Oil vapor was the main concern, after all water is not toxic so it wasn't given much thought until tanks started blowing up. Instead of going to better filter systems, lined steel tanks and aluminum tanks were supposed to solve the problem. Blowing water into tanks from wet fill whips also contributed to the problem so wet filling was stopped but it has it's advantages if done properly by not allowing the tank valve and whip to ever go under water.

 

[JamesBon92007]

I think this rust issue stemmed from the frequent practice of the era, to wait for your last breath, pull the j valve, shoot one more fish or grab one more bug, then free ascend with an empty tank....Many people back in the 70's would ALWAYS stay down till the tank was empty--that is what signalled the end of the dive..salt water could enter the tank...and this was bad for the steel 72's

And nobody does that anymore, right?

I started buying aluminum tanks because I needed more tanks and they were cheaper. They were also supposed to last forever (or at least a lot longer than the steel tanks of the day). Meanwhile, my old steel tanks still pass hydro and VIP and only one of my AL80s looks good enough inside for me to even consider using. I seem to remember the dive shop saying the ALs weren't going to be needing annual VIPs either so that was also a cost consideration. As it turns out they not only need the VIP and hydro they also need a Visual Eddy test.