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-   -   Devil bacteria in Corny kegs (http://www.homebrewtalk.com/f11/devil-bacteria-corny-kegs-388294/)

JuanMoore 03-21-2013 05:35 AM

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Yes, you're totally misunderstanding things.

Originally Posted by Aloha_Brew View Post
Beer isn't being pressurized back into the line but is rather being sucked in due to the differential pressure occurring, only when I initially pressurize or dispense I'm guessing since I see no other way this would occur.
This makes zero sense. Yes, it's a pressure differential causing the flow, meaning that the pressure on one end is higher than on the other end. You can think of it as either the lower pressure on the regulator side creating a relative vacuum and "sucking" things towards the regulator, or as the higher pressure on the keg side pushing things towards the regulator, but it's the same thing.

Originally Posted by Aloha_Brew View Post
From what I know of check valves, they only work when the pressure on the opposite side of the source (in this case, the keg with beer) is greater, to protect the source (the gas source).
Yes, that's exactly how they work. A check valve, when functioning properly, only allows flow in one direction. When the pressure on the gas tank side is higher than the pressure on the keg side, the valve opens and allows gas through. When the pressure on the keg side is higher than the pressure on the tank side, the valve closes and doesn't allow anything to flow through. I'm not sure what type of filter you think would allow gas through, but not beer, and yet not completely clog and block all flow the first time beer touches it.

There are many types of check valves, but here's how ball and spring check valves work. With pressures equal on either side, the spring pushes the ball against the seat, closing the valve. As long as the pressure on the left is higher than on the right, the valve will remain closed. The pressure on the right has to be high enough compared to the left to push the ball against the spring hard enough to open it. The pressure required to do this is called the cracking pressure. The cracking pressure for the ones I use is 1psi, which means that with the regulator set to 13 psi, the keg pressure has to drop below 12psi before the check valve will open and allow gas through.


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