New CO2 tank need purging?

[rcrabb22]

When I have bought a new 20lb propane tank the guy at propane supply said a new tank needed to be purged and charged me an extra $5 to do it. It was a similar process to purging the O2 from head space of a keg. A little propane in, release, repeat 2 or 3 times if I remember.

Do I need to have the same purging process with CO2 done for a brand new CO2 tank the first time it is filled?

 

[subliminalurge]

IMHO, not really, unless you're really anal...

It has regular air in it right now, at atmospheric pressure. It's going to get "pure" co2 in it at around 800 psi. That air that's in it will shrink at that pressure to a tiny, tiny portion of the total amount of gas in the tank.

I also have other reasons for not worrying about it, but since I'm not an expert and don't know for sure that I'm right, I won't go into details on those....

 

[audger]

A little propane in, release, repeat 2 or 3 times if I remember

whats that about propane? you didnt pay $5 to have your CO2 tank purged with propane i hope...

they purge the tank when they fill it anyway. if you dont, then you cant fit the whole 20lb in it, as gas pressure would keep the liquid out. so half way thru, they purge the gas to let more liquid in. you paid $5 for nothing.

 

[shortyjacobs]

Yup. If you've ever filled your own CO2 bottle, you'd see that "purging" is standard practice anyway.

You have to have the tank COLD to get it "full" of CO2, (actually, only about 60% full by volume....the rest is left as gaseous CO2 to account for thermal expansion). To get it cold, you can either stick it in a very cold freezer for a while, or, (much easier, and what all CO2 fill stations do), put a bit of CO2 in it, then vent it quickly. The expansion of the liquid CO2 to gas and down to atmospheric pressure chills the bottle quickly, allowing you to fill it with liquid CO2 to capacity.

 

[rcrabb22]

whats that about propane? you didnt pay $5 to have your CO2 tank purged with propane i hope...

they purge the tank when they fill it anyway. if you dont, then you cant fit the whole 20lb in it, as gas pressure would keep the liquid out. so half way thru, they purge the gas to let more liquid in. you paid $5 for nothing.

No I haven't filled the CO2 tank yet.

When I get my propane bottles filled they put it on a balance scale with a preset tar weight value (the weight slide is at 41 lbs) and they fill until it tips the scale or the OPD valve closes. Usually the scale tips first but one of the three tanks never tips the scale and OPD valve stops the process. They never purge it during the fill process.