Which tanks to choose

[rx7diver]

Well hydro is like 5/3's the working pressure, and the blast pressure is well above that.

Hmmm. I think the 5/3's working pressure thing applies to 3AA (and 3AL?) scuba cylinders. Does it apply to modern HP cylinders, too?

rx7diver

 

[GiraffeMarineSalvage]

Important side note for people newer to choosing tank fill pressures, there are numerous SB threads on "cave fills" and the like for you to make your own personal informed decisions (in short increased safety of more gas but decreased tank safety margins and theoretically/maybe shorter lifespan ie really long to really long minus a little...) but it's important to note regularly overfilling steel tanks (especially some of the extremely conservative low pressure tanks) is very very different than regularly overfilling aluminum tanks (and Ross19966 is spot on filling in a water bath, I wish dive shops weren't so adverse to that common sense option to keep tanks cool while filling...)

 

[rob.mwpropane]

Might need to make a field trip over your way to pick your brain. You're only a couple hours away.

You are more than welcome... not much left but happy to help!

Hmmm. I think the 5/3's working pressure thing applies to 3AA (and 3AL?) scuba cylinders. Does it apply to modern HP cylinders, too?

rx7diver

If I'm being honest I'm not sure, but I know it's a lot more then I pump my tanks to

 

[Thunder Struck]

100cf actual from 77cf actual is 30% more.

Thanks, I was starting from the other direction as the AL80 was 77% of the HP as whole.

 

[Tracy]

For 95% of divers in the US. The HP100 is an ideal tank. Whether they can fill it to max pressure doesn't really matter. It is a ideal sized light weight tank with good buoyancy charachteristics. Buying a new low pressure tank unless it is considerably cheaper never makes sense. Even if they only fill it to 3000 psi, that is still more gas than the comparable LP tank when filled to rated pressure.
There aren't many shops in existence that can't fill to at least 3000 psi. You do still find some with 3200 psi machines, but they are rare at this point.

 

[rx7diver]

For 95% of divers in the US. The HP100 is an ideal tank. Whether they can fill it to max pressure doesn't really matter. It is a ideal sized light weight tank with good buoyancy charachteristics. ...

The "problem" with my Genesis PST HP100 cylinders (3,500 psig) when I owned them was that they (arguably) were too negatively buoyant for me to use as singles in MO/AR freshwater lakes--unless I was wearing a wetsuit of at least medium thickness.

On the other hand, an old-school 72 is perfect for me for this. Mine is a U.S. Divers-stamped PST cylinder having a 1970 original hydro--one of the very few pieces of gear I've purchased used.

rx7diver