A fluid flow control apparatus for use in, for example, a patient interface, is provided that includes a main conduit structured to receive a pressurized fluid and a nozzle assembly coupled to the main conduit. The nozzle assembly includes an external nozzle element having a contoured top surface and a main bore in fluid communication with an interior of the main conduit, an internal nozzle element received within the main bore, wherein a gap is provided between the internal nozzle element and the external nozzle element, and a switching element selectively moveable between a first position and a second position, wherein in the first position, the switching element is positioned below the contoured top surface of the external nozzle element, and wherein in the second position, at least a portion of the switching element is positioned adjacent to or above the contoured top surface of the external nozzle element.
