What is the name of the part in the draft system that allows gas to flow in and out?

The coupler is the part of the draft system that allows gas to flow in and out. It serves as the connection point between the keg and the draft lines. When the coupler is engaged, it opens both the gas and beer ports, allowing carbon dioxide to push the beer from the keg through the lines and into the tap. The design is crucial for ensuring that the beer maintains its carbonation and flows properly while preventing contamination.

The coupler's function is distinct from that of the regulator, which controls the pressure of the gas coming from the CO2 tank, and the keg tap, which is the physical outlet where the beer is dispensed. The CO2 tank provides the source of gas, but it is the coupler that actively enables the gas flow necessary for the system's operation. Thus, its role is vital in maintaining the integrity and functionality of the draft system.