First time kegging, some questions.

[javert]

This is probably a bit silly but it's the first time I'm going to serve beer from a keg and don't want to bring a good batch to waste.

I'm fast carbonating according to this video. To sum it up, set the pressure to 25 psi, rocking the keg for 200 s, disconnecting from the gas tank and put it to chill in the refrigerator (not going to drink it in 30 minutes, though, but this Friday) before connecting it again to the gas line and adjust the pressure to serving.

My questions are:
If the keg is pressurized at 25 psi and I'm going to serve at, say, 12 psi, should I relief the pressure from the valve before connecting the gas again?
I have a ball-lock model, is the gas coupler a one-way valve or is there the risk of beer back flowing to the gas tank if the keg pressure is greater?
Doesn't relieving the pressure in the keg undo the carbonation of the beer? How do I know the keg is equilibrated to the gas tank pressure when using the relief valve?

 

[beermanpete]

If the keg is at a higher pressure than your line it might vent some gas through the regulator (to atmosphere) but not beer as long as the keg is vertical and not over filled. There is no check valve in the keg to prevent this but some regulators do not vent under this condition due to their design. After you fast-carb the beer and remove the gas line the gas in the headspace will continue to dissolve into the beer and by the time you are ready to serve the pressure will likely be low enough that there will be no issue. It may end up being under carbed.

Relieving the pressure from the keg is no different that opening a bottle; the head space is vented but the beer stays carbonated for a while. It is not a problem to vent the keg to connect the gas line and then re-pressurize it shortly thereafter.

 

[brew703]

My process is I set my pressure to 30 psi for 30 hours then set my regulator to 14-15 psi and purge the keg until gas starts flowing back in the keg. I do this a couple times over the course of 24 hrs. Usually a day after I reduce to service pressure beer is perfectly carbed. So about three days after racking to keg my beer is good to go. Sometimes a bit green but still drinkable.

I've heard of beer flowing back through the gas line into the regulator. Never happened to me. I don't connect my liquid line until I'm at serving pressure.