Which device prevents beer from backing up into the gas line when the coupler is disconnected?

A check valve is designed to allow fluid to flow in one direction while preventing backflow. In the context of a beer dispensing system, when a coupler is disconnected from a keg, it is essential to prevent beer from flowing back into the gas line, which could lead to contamination or other issues. The check valve serves this purpose by blocking the reverse flow of beer into the gas line, effectively maintaining the integrity and cleanliness of the system.

The other devices mentioned serve different functions. The Sankey valve, a type of coupling device for kegs, facilitates the dispensing of beer but does not specifically prevent backflow into the gas line. A CO2 tank provides the necessary carbonation for the beer but is not involved in controlling backflow. Finally, a pressure regulator manages the pressure of the gas supplied to the system but, like the Sankey valve, does not prevent beer from backing up into the gas line. Thus, the check valve is the specific component that fulfills the requirement of preventing backflow when the coupler is disconnected.