pv=nrt

[StLouBrew]

I really should've paid more attention in school. Apparently I didn't give Mr. Boyle my Constant attention...

Today I went running back to the one and only place in St. Louis that actuall fills CO2 tanks while you wait, because I thought I had depleted the majority of the tank I had just filled last week. I did this because I noticed that the tank PSI reading on the guage had gone from somewhere near 1800 to down to just below 1000. This is where it's worth noting that the 1800 reading was at room temp and the less than 1000 was after it was in the fridge.

After seeing that reading I did the bubble test and saw that I had a slow leak. I thought I'd nearly spent the tank. But.. after weighing the tank at re-checking the guage with the tank at room temp... a friggen miracle - back up to nearly 1800.

I guess I would've expected some difference in the reading based on the temp, but not that much. So... bottom line, are all tank guage readings meant to be taken at RT?

Cheers

 

[Yooper]

The weight should be the same, regardless of temperature.

There is a great way to deal with the high pressure gauge in situations like this- cover it with duct tape.

Since c02 is a liquid dispensed as a gas, the temperature will impact the reading on that gauge. It'll read "500 psi" forever- then go to 0 in 15 minutes when it runs out of gas. It's not really like a fuel gauge at all. Weight is the only way to know how much gas you really have.

 

[blakelyc]

Not really.... The gauge pressure in the tank is the gauge pressure in the tank. pv=nrt, which also means p=nrt/v. So, for a constant volume of gas, there in a proportional relationship between pressure and temperature. Lower temp means lower pressure.

That's not to say that there is "less gas" since the mass didn't disappear, but rather that pressure isn't a measure of volume or mass.

 

[StLouBrew]

There is a great way to deal with the high pressure gauge in situations like this- cover it with duct tape.

Hey Yooper! Thanks for the response. I've read a ton of your posts... Big fan here :rockin:

Going forward, I'll go by weight and ignore the tank PSI guage.

 

[Yooper]

Hey Yooper! Thanks for the response. I've read a ton of your posts... Big fan here :rockin:

Going forward, I'll go by weight and ignore the tank PSI guage.

Thanks for the nice words! I'm in St. Louis myself at the moment. Well, sorta. We're on the outskirts, near E. St Louis, and will drive through tomorrow AM on the way south. I keep saying that I would love to stop at the AB beer tour, but we won't stop.

My current favorite St. Louis area beer is Schafly. I can't seem to find it in gas stations, though- any tips on a place on I55 to find it? Thanks!

 

[StLouBrew]

My current favorite St. Louis area beer is Schafly. I can't seem to find it in gas stations, though- any tips on a place on I55 to find it? Thanks!

There are two chains of local grocery stores that carry Schlafly - Dierbergs and Schnucks. And.. if you ever get back this way, the A/B tour is cool, but Schlafly does tours too.. and the samples are WAY better!

Safe travels Yoop!!