When to choose a lower capacity tank

[TSandM]

If I were only going to own two tanks, I'd buy HP 130s. Nobody ever had a problem due to having too much gas. The 130s are heavy and massive, but not that much more than my LP95s are, and they do hold much more gas.

I do sometimes wish I had a set of HP100s, because the vast majority of the shore dives I do can be done on 100 cf of gas, and they are quite a bit lighter than the 130s to lug around (lighter than the 95s, too).

I wouldn't double up 130s, though, unless you are doing significant staged decompression dives. My dear dive buddy, who is six feet tall and strong as an ox, dove doubled 130s for a couple of years. Then he got a set of LP72s for his son, and discovered how nice it is to carry much lighter tanks into the water -- you don't see him in the 130s for anything but major dives any more!

 

[FritzCat66]

FWIW, the HP120 seems to have the single best efficiency in terms of capacity vs. raw cylinder weight, about 3.17cf per pound at the rated pressure of 3442psi, at least out of the current crop of Worthington cylinders. It's also the largest capacity tank in the narrower 7.25"-diameter size, which fits most boats without problems where the larger 8"-diameter tanks sometimes make trouble. Most of the other HP tanks seem to achieve ratios around 3.0 cf/pound.

At their rated 2640psi, no LP tank comes anywhere close to that efficiency, only about 2.2-2.4 cf/pound. Even with a 3000psi overfill, they still don't break 3.0cf/pound.

But... the HP120 is too tall for many folks, only surpassed in height by the 8"-diameter LP121. And at 38 pounds empty, the HP120 is still no lightweight (although an AL80 is about 31 pounds, and the similar-capacity LP108 is nearly 46 pounds). Caveat emptor.