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if the OP lives in cave country and intends to dive caves, he needs to do his tank choosing from a different perspective
Not necessarily. Just because people will fill LP tanks to 4000 PSI doesn't mean you have to have yours filled to that pressure.
If I'm sitting on LP 104s with 3,600 to 3,900 and my buddy shows up with 2,640, I'm going to send him back to the dive shop to get his tanks filled. As someone else said, 2640 is turn pressure, not starting presure.
Yikes this turned into a long thread....
3900 psi in a tank with a 2400 psi service pressure is a 65.5% overfill. The hydro test pressure for that same 2400 psi tank is 4000 psi - a pressure acheived with water pressure not air pressure for safety and a pressure the tank is only intended to hold for a few seconds.Yes, but everyone does. If you don't, you'll be limiting yourself dramatically and turning a lot of dives early. I suspect, you will also find it hard to find a buddy, though I don't really know for sure because I've never ran into anyone that didn't overfill.
If I'm sitting on LP 104s with 3,600 to 3,900 and my buddy shows up with 2,640, I'm going to send him back to the dive shop to get his tanks filled. As someone else said, 2640 is turn pressure, not starting presure.