How much air in a low filled HP80

[dmdalton]

sheck33 once bubbled...
what i was trying to say is the following, if i fill a tank to say 3800 PSI, close the valve, take it to the beach and then i attach my SPG it might give me a 3500 PSI reading, you can use any formula you want but the amount of air, as in the amount of air molecules, is the same.

Dmdalton, your statement is incorrect:

When the temperature rises the pressure rises in a scubatank, the volume however does NOT change, the volume is fixed since the tank is a RIGID metal container.


Also dont forget that the SPG is a pressure gauge and NOT a content gauge.

).
You are correct, I mis-spoke (my whife would love to hear that)

Volume was the wrong word to use. Volume (water capacity) of a tank does not change with temp. Volume (molecules) of the air inside the tank also does not change. Free air delivery (thank you Omar) does and that was what I was after.

Also correct that SPG is a pressure gauge (hence it's name "submersible pressure gauge") however it is converted to a contents guage through the dive planning process (today I am diving double tanks that combined hold a total of 190 cu ft @ 2640 psi, therefore when psi is at 1000 psi I will have 72 cu ft of air left).

Dave D