Help with understanding

[schmidtwit]

Hi all. I have decided to venture in to kegging with mini 5L kegs for small batches (for a variety of reasons). Looking to build a set up similar to this (scroll to the "building the keg tap"section:
http://www.angelfire.com/cantina/carbonation/TappingandDispensing.htm

My question is more technical than anything. In looking at the diagram and am failing to understand how, with a single copper dip tube, one accomplishes both the pressurization with CO2, and dispensing of the beer. If the tube is under gas pressure, what permits the beer to come up?

I know this is probably really stupid, but can anyone help me understand better?

 

[JINKS]

The way I see it is the tube isn't always under pressure from the external co2. You pressurize the keg by squeezing the trigger on the tire inflator, which pressurizes the keg, then when you release the trigger, the internal pressure of the keg is now greater than the external atmosphere so it wants to come up and out of the tube when you open the tap on the other end.

If you blow a balloon up and keep it in your mouth but release pressure through your nose is a good example of how this principle works.

 

[schmidtwit]

That makes sense, except for where he mentions you can replace the Schrader valve to direct connect to a co2 tank. Wouldn't this then mean the keg is under constant pressure?

 

[JINKS]

After looking closer I see there is an inner and outer dip tube, looks like the vinyl tubing attached to the the tap runs all the way down through the dip tube and into the beer. See blue lines in bottom of his pic pointing to 2 different parts of the setup.

 

[schmidtwit]

Aha! Good eyes good sir. Much obliged.

 

[zachattack]

Also there's a hole drilled near the top to allow gas to enter the headspace but beer to flow through the longer tube.

Either way I wouldn't want copper in contact with finished beer for very long.