Filtering facepiece respirator with an adjustable inhalation-exhalation valve

A filtering facepiece respirator comprising:

• a facemask adapted to fit over the nose and mouth of a wearer, the facemask comprising a mask body containing a filtering structure;
• a harness coupled to the mask body for securing the facemask on the face of the wearer;
• and
• a mechanical valve coupled to a portion of the mask body proximate the wearer's mouth, the valve being manually adjustable between a first mode of operation and a second mode of operation, where in the first mode of operation air is permitted to flow through the valve on exhalation but not on inhalation and in the second mode of operation air is obstructed from flowing through the valve on exhalation and inhalation,
• where the valve comprises a valve housing having an interior chamber, a fixed hub member disposed within the chamber, a first movable hub member disposed within the chamber, a pliable diaphragm disposed between the fixed hub member and the first movable hub member, a screw member disposed within the chamber extending along a longitudinal axis of the valve housing, and an adjustable dial, the adjustable dial being rotatable about the longitudinal axis, where the adjustable dial is coupled to the screw member and the screw member is threadedly coupled to the first movable hub member such that when the adjustable dial is rotated by the wearer, the screw member is also rotated and the threaded engagement between the screw member and the first movable hub member causes the first movable hub member to translate axially along the longitudinal axis away from or towards the fixed hub member.