A valve arrangement for a patient interface device for use in delivering a flow of breathing gas to an airway of a patient, the patient interface device comprising a sealing portion adapted to sealingly engage about at least a mouth of the patient and a frame portion supporting the sealing portion and defining a cavity therein which is adapted to receive the flow of breathing gas prior to passing to the airway of the patient, the valve arrangement comprising: a valve member having a coupling portion and a blocking portion extending from the coupling portion, the coupling portion being structured to be coupled to the frame portion, the blocking portion being structured to sealingly engage about an aperture which is defined in the frame portion and which provides a passage between the cavity and an exterior environment, the blocking portion being structured to move between: (i) a first position wherein the blocking portion seals about the aperture and prevents the ambient air from passing through the aperture, and (ii) a second position wherein at least a portion of the blocking portion is spaced from the aperture, thus allowing ambient air to pass through the cavity into the aperture, and characterized in that the valve arrangement further comprises: a guard member having a coupling portion and a protecting portion extending from the coupling portion, the coupling portion being structured to be coupled to the frame portion, wherein in use, when the valve member and the guard member are coupled to the frame portion, the protecting portion of the guard member is positioned and structured to be disposed between the blocking portion of the valve member and the mouth of the patient when the sealing portion is sealingly engaged about the at least a mouth of the patient, and wherein, when the blocking portion of the valve member moves from the first position toward the second position, the blocking portion moves toward the protecting portion of the guard member. a valve member having a coupling portion and a blocking portion extending from the coupling portion, the coupling portion being structured to be coupled to the frame portion, the blocking portion being structured to sealingly engage about an aperture which is defined in the frame portion and which provides a passage between the cavity and an exterior environment, the blocking portion being structured to move between: (i) a first position wherein the blocking portion seals about the aperture and prevents the ambient air from passing through the aperture, and (ii) a second position wherein at least a portion of the blocking portion is spaced from the aperture, thus allowing ambient air to pass through the cavity into the aperture, and characterized in that the valve arrangement further comprises: a guard member having a coupling portion and a protecting portion extending from the coupling portion, the coupling portion being structured to be coupled to the frame portion, wherein in use, when the valve member and the guard member are coupled to the frame portion, the protecting portion of the guard member is positioned and structured to be disposed between the blocking portion of the valve member and the mouth of the patient when the sealing portion is sealingly engaged about the at least a mouth of the patient, and wherein, when the blocking portion of the valve member moves from the first position toward the second position, the blocking portion moves toward the protecting portion of the guard member. (i) a first position wherein the blocking portion seals about the aperture and prevents the ambient air from passing through the aperture, and (ii) a second position wherein at least a portion of the blocking portion is spaced from the aperture, thus allowing ambient air to pass through the cavity into the aperture, and a guard member having a coupling portion and a protecting portion extending from the coupling portion, the coupling portion being structured to be coupled to the frame portion, wherein in use, when the valve member and the guard member are coupled to the frame portion, the protecting portion of the guard member is positioned and structured to be disposed between the blocking portion of the valve member and the mouth of the patient when the sealing portion is sealingly engaged about the at least a mouth of the patient, and wherein, when the blocking portion of the valve member moves from the first position toward the second position, the blocking portion moves toward the protecting portion of the guard member.