So I have this very old 15 gallon steel CO2 tank that I filled about 15 years ago. I plugged it in and just read about 750 psi. I thought it was nearly empty because as I recall from SCUBA, I would start with 3000 psi and then watch the pressure go down and when it got to 500 psi it was time to come up. So I assumed that CO2 was similar. Then I read here something different:
How Many Kegs Per CO2 Cylinder
A gas tank that is properly filled should read about 750 PSIG when the cylinder is at a 72°F temperature. CO2 gas pressure increases when it is exposed to heat, so if the gas tank temperature is above 72°F, the pressure will read higher than 750 PSIG. If the gas tank temperature is colder then 72°F, the pressure will read lower then 750 PSIG.
The tank pressure should read 750 PSIG until the liquid CO2 in the cylinder is gone, and the tank is almost empty. A decreasing pressure indicates the cylinder is nearly empty.
So the pressure won't drop because it's liquid right?
How do I know what's left? Is there a tank weighing rule?