| 摘要 |
<p>A respirator (10) providing a dust mask includes a central exhalation valve (26) and a concentric inhalation valve (34) the inhalation valve (34) leading to a filter assembly comprising a perforate retaining member (42), a filter (44), a frame (14) and an imperforate back wall (30), the filter (44) and back wall (30) being separated by buttresses (24) of the frame (14) which afford a passage for air to the inside of a face piece (12).</p> |
