A breathing system with a facepiece that includes a first port adapted to be placed in fluid connection with the outlet of a regulator assembly to introduce pressurized breathing gas into the facepiece; a second port adapted to be connected to an air purifying system; and an exhaust valve through which the user's exhausted breath can exit the facepiece. The breathing system also includes a pressure adjustment mechanism that includes a communication link in communicative connection with an actuator such that the exhaust pressure adjustment mechanism sets the internal facepiece pressure required to open the exhaust valve, independently of the respiration of the user, to a first pressure when the actuator is in the first state, to a second pressure when the actuator is in the second state. The first pressure is higher than the second pressure.