too big? 120, 130 larger What is a good size.

[kwinter]

AFAIK they are cheaper than steel cylinders

No, they ARE steel cylinders. Some people like the trim characteristics. Others like having a low pressure (2640 psi) tank they can "cave fill" to 3000 or 3500 psi and have lots of capacity. Using HP tanks can often leave you with a short fill, while LP tanks don't usually have that problem.

 

[jcaplins]

The bottom three are all listed12.2 l yet the first of those lists a higher pressure to make 80 cu ft. Surely some mistake?

Btw, what is it with these LP tanks? Are they physically lighter than similar water capacity HP ones?

No mistake (AFAIK). The internal volume is the same. The HP100 tank has a larger outside diameter, a little shorter, but is a lot heavier than the LP72. A lot more steel there to handle the extra 1000psi.

The bottom 2 are the same tank, I just created a second line to take the '+' rating into account.

 

[kelemvor]

I've got LP tanks. Only for the "cave fill" benefits. I routinely get fills at my LDS to 3400. In cave country they typically fill to 3800. Disks haven't been changed, I can't believe they haven't burst yet.

If your shop isn't overfilling I would get the HP tanks. Just comparing worthington lp95 to hp100, the full buoyancy between the two is almost identical -10.0 vs -10.1. However the HP100 is only 33lbs empty on the surface while the lp95 is 41.9. Other manufacturers probably have different specs, but Worthington is what I had on hand.

It's also worth checking the tank diameter. Most LP tanks I've seen are 8" and HP100's tend to be 7.25" (same as al80's). This means the HP100's will fit in tank holders on boats more easily and you don't have to adjust your bcd tank straps if you switch to a rental tank for some reason.