warm kegging?

[bub]

I fill the keg with CO2 from the beer outlet (dip tube side) and pressurize, then I slowly let the release valve open for a few seconds (20-30 should do it) pull off the co2 and depressurize with the release, and you should be good to go.
BUB

[DannyW]

I am not a physicist (nor do I play one on TV) but I thought purging an air filled container through cycles of pressurizing and venting was not very effective at the pressures and number of cycles that we use. I vaguely remember that hundreds of psi and dozens of cycles were required to get down to something like four 9's of purge.

I've googled for a reference, but come up empty, so maybe I'm making the whole thing up

I usually wait until I have a bunch of clean, empty kegs that need purging and make up 5 gallons of iodophore or starsan. Fill the first keg right to the top and then push serially through all the kegs in turn. After each one appears to be empty I let it sit for several minutes, then vent it out the out tube one more time to get any sanitizer that has dripped down and collected in the bottom. After this I never find more than a couple of ml in the bottom, and I don't see how there could be less than 100% CO2 filling the head space.

[bub]

well you can make sure by doing this....
take lid off keg
put co2 on diptube side
light match
turn on co2
place match in top of keg.... when match is out co2 is in keg...
CO2 is heavier than air so if you do it the way I posted you should be gettin most of the air out anyway.
BUB

[DannyW]

Mixing and gas-law stuff gets in the way of the (old wives tale?) of heavier CO2 sinking immediately to the bottom of the keg. If CO2 is heavier, then why doesn't a cylinder of beer gas dispense CO2 first and then N2? It dispenses pretty much the same blend from first use to last, right?

I found a lively discussion on this topic over at probrewer.com.

Siebel's notes say a tank can be “...purged with CO2, but this is an inefficient and ineffective way to achieve the CO2 atmosphere. The most effective way is to fill the tank with water, push the water out with CO2 and the fill with beer.”

The match test might show you that you have a certain minimum concentration of CO2 but not that air/oxygen concentration is approaching anything near 0%. The same thread linked above says death to humans (and I presume extinguishing of a match?) happens at 10% CO2 - far below the concentrations we seek in the headspaces of our kegs.

Of course, this is all nit-picking. Pressure-and-vent works well enough (for some value of "enough") for most of us. It's just so much fun to pick Bub's nits