How long does a keg keep pressure?

I'm going away for the holiday weekend, and thinking of bringing a corny with me, my hope is to just keep it on ice and use a picnic tap. Can I expect the keg to hold it's pressure all night? I have a 20lb tank, so I'd rather not bring it if I don't have to.

 

You could buy one of those pocket sized keg dispensing CO2 chargers. Otherwise, I would not expect very long, unless you pre-pressurized it pretty high. And then the serving pressure won't be even throughout the night - you could have alot of foam at first.

 

If there is no leak and the beer is fully carbonated, It'll hold it's pressure right around forever... but, as you dispense that pressure will go down so you would need a source of new pressure.

The small CO2 cartridge thing is great for a trip (be sure to bring an extra cartridge or two, just in case one dumps out by accident or you run out.

http://morebeer.com/view_product/18301/102290/CO2_Injector_Ball_Lock

 

If you must do it, then carb it up cold to 20 psi for a week before hand. Then it will last longer before going flat. Might have to use a pitcher though.

 

use gas law properties to determine how long the keg will keep pressure. if you have a 5 gallon keg with 4 gallons of liquid in it, and you pressurize the 1 gallon of headspace to 10psi, then you would have 5psi in the headspace after you draw off 1 gallon...

1gallon of headspace @ 10psi
=2gallons of space @ 5psi
=4 gallons of space @ 2.5psi
...etc

if your keg is filled all the way to the top, you might only have a pint of headspace. so replace "gallon" with "pint" in the above example. so you will have 2.5psi left after only 4 pints are drawn off.

 

I wanted a keg charger for this, but eventually realized a couple of growlers are so much easier. So that's what I do. A keg charger sounds perfect for what you are looking for though.