How does a FOB work?

I know what a FOB (foam-on-beer) does. It basically prevents foaming on a long draw draft system. I just don't understand how it works. What is the engineering behind it that allows it to separate the foam and excess gas from pure beer?

dgilly said:

I know what a FOB (foam-on-beer) does. It basically prevents foaming on a long draw draft system. I just don't understand how it works. What is the engineering behind it that allows it to separate the foam and excess gas from pure beer?

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It doesn't prevent foaming or separate foam from beer, it simply closes the line when a keg kicks, so that the lines don't fill with foam. It's a simple float valve, so as long as beer is flowing the float lifts up and allows the beer to pass through to the faucet, but when the keg kicks and starts sending foam, the float drops down and closes.

If you're having issues pouring foam with a full keg, a FOB system probably won't help any.