The respiratory protective device minimizes dead space by locating the exhalation valve mechanism slightly spaced from, but directly in front of the mouth. The inhalation valve mechanism surrounds the streamlined flow path leading to the exhalation valve mechanism. The inhalation valve mechanism is located...http://www.google.fr/patents/US5086768?utm_source=gb-gplus-shareBrevet US5086768 - Respiratory protective device
