Located on the cooker/canner cover, the vent pipe allows excess pressure to be released. It is also what the pressure regulator sits on. Compatible Products 16-Quart Pressure Canner 01/CA16A 16-Quart Pressure Canner 01/CA16H 21-Quart Pressure Canner 01/CA21H 21-Quart Pressure Canner 21B 16-Quart Pressure Canner 7B