What is the name for the part of a draft system that automatically stops the flow of beer when the keg empties?

The part of a draft system that automatically stops the flow of beer when the keg empties is known as a FOB, which stands for "foam on beer." This device is essential in draft systems because it helps to prevent waste and maintain beer quality. When a keg runs out, the FOB detects the loss of beer and stops the flow, preventing excess foam or air from being drawn into the lines. This is particularly important in maintaining consistent beer delivery and avoiding spills.

In contrast, a beer pump is typically used to manually draw beer from a keg rather than automatically stopping the flow. The coupler is the device used to connect the keg to the draft system but does not control flow based on the keg's contents. The faucet is the tap that dispenses beer but does not have the function of detecting when a keg is empty. Thus, the FOB is a vital component in ensuring efficient and quality service in draft beer systems.