Abstract: A breathing apparatus includes a tank containing pressurized breathing gas, a regulator having an inlet connected to the tank, an outlet for providing breathing gas to a user, and a valve configured for controlling a flow of breathing gas between the inlet and the outlet. A facepiece includes a first port for connecting with the outlet of the regulator, a second port adapted to be connected to an air purifying system, and an exhalation valve. A pneumatic pressure adjustment assembly is in operative connection with the exhalation valve, and has a first pneumatic connection in operative connection with a second pneumatic connection in the regulator. The pneumatic pressure adjustment assembly is operable to adjust the internal facepiece pressure for opening the exhalation valve based on whether breathing gas is delivered to the pneumatic pressure adjustment assembly. An alignment mechanism is provided for aligning the regulator with the facepiece.