CO2 Question for those wiser than I

[Voodoo Lounge]

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[Acmemfg]

High School Physics-Charles' Law...

"At constant pressure, the volume of a given mass of an ideal gas increases or decreases by the same factor as its temperature on the absolute temperature scale (i.e. the gas expands as the temperature increases).

Wish I had paaid more attention to this sort of thing my senior year; I didn't realize all this would be so relevent to draught beer!!

[psychodad]

In any case I suppose that physics stuff just about renders the high pressure gauge worthless. I have a full 20 lb. tank with the needle on the gauge quietly resting just before the red zone.

Not really. That needle will hover above the red area for some time. While it will tend to dive quickly once it is in the red area, it is not an immediate thing and gives you some time to prepare to have a tank filled or get an exchange.

[cubby_swans]

That reading is directly related to the tank's ambient temperature. It will stay steady until the tank runs out of liquid co2. At that point you will be depleting the co2 gas and the pressure reading will start to dive. With a 20 pounder, once it starts to dip you will be pouring beer for days before it's actually empty, unless you have a party or something and the beer is flowing freely. My 5lb tank lasted me over a week once I ran out of liquid co2, and I pour a few pints almost every day, and quite a few pints on the weekends.

[Acmemfg]

Yeah, as long as the temperature is constant, pressure will not increase, but will decrease as the CO2 volume gets lower. Not unlike putting a can of soda in a very hot car interior for a few hours in the middle of July. Temperature increases, gas (carbonation in the soda) expands, can explodes...makes huge mess. Same concept.