5lb co2 tank issue

[keirnan]

Hey! After dragging refilled tank around all day yesterday, I hooked it up and the gauge read 900. I have no idea what a freshly filled tank is supposed to read. This morning the same gauge read 750. So I tested the tank for leaks and found none.

Can anyone familiar with this situation shed some light on what may be happening?

Thanks in advance!

 

[dinokath]

I am no pro, but that gauge is very dependant on the temperature of the CO2 tank itself. For example, my tank reads one pressure when outside the keg and another pressure when at keg temps. The folks at the CO2 filling store will fill it to capacity by weight, not by pressure. I say roll with it if they just filled it. Too much pressure and it will blow the safety and you'll lose all that gas!

Again, I am no pro, but I have read that if there was an option to remove that gauge it should be done, which begs the question, from me, why even put it on there to begin with? Again, I am no pro!

 

[Yooper]

If it dropped from 900 to 750 psi, it sounds like you put it in the fridge or it otherwise got colder.

Those gauges are useless, by the way. It'll read 500 psi for a long time, until it's completely empty, then it will suddenly drop to 0.

 

[user 21663]

Best way to gauge is weigh it and subtract the Tare weigh of the canister. The gauges never are accurate for me ( except when the stupid thing runs out on a Saturday right after the gas store closes, then it reads 0. ggrrrrrr... ).

 

[Bentpirate]

My experience with gases comes from scuba diving. When filling tanks the gas (CO2, O2, HE, etc) will heat up and expand, causing a 'false' higher pressure reading. Once cooled the pressure will equalize with the ambient temperature. The best fills are slow and not rushed. Your pressure changes on you gauge are from the ambient temperature acting against the inside temperature. Exactly what steveo155 says, best gauge is measure volume in pounds.
Boyle's law (sometimes referred to as the Boyle-Mariotte law) is one of many gas laws and a special case of the ideal gas law. Boyle's law describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system.

 

[SweetSounds]

CO2 is a funny gas - The pressure in the tank is directly related to the temperature. So at 80 degrees, it can be 900 PSI, and in the keezer at 40 degrees, it can read 400. Your high pressure gauge is literally only good as a thermometer! You need to weigh the tank (without the regulator), and subtract the tare weight stamped on the bottle, to see how much gas (In the form of liquid CO2!) is left in the bottle.

Assuming the temperature stays the same, the pressure of the CO2 will not change if it's got 200 pounds or 1/4 pound of liquid CO2.

When all of the liquid CO2 has changed to gas, and gone out to your beer, THEN the high pressure gauge will start to drop - And it'll drop fast. Then you'll have a few glasses of beer before it's gone entirely.

 

[akthor]

Yeah the 2nd guage is pretty useless it just tells you yes there is gas or no there is none pressures don't matter since co2 is liquid till the end just about. The guy at the welding shop explained it to me.

 

[Beerrific]

CO2 is a funny gas - The pressure in the tank is directly related to the temperature.

This is true for all [ideal] gasses. It can easily be expressed:

http://en.wikipedia.org/wiki/Gay-Lussac%27s_Law.

 

[keirnan]

Thank you all for the responses! This is a really great site, especially for beginners.