US Patent 7395835 Air admittance valve

In some embodiments, an air admittance valve includes a base, a screen plate and a diaphragm engageable with the screen plate. The diaphragm may include a first center disk having a stem and a membrane coupled to the first center disk. The membrane may have a continuous material sized to extend beyond a perimeter of the first center disk, be formed of a material more pliable than the first center disk and be adapted to be coupled to the first center disk through the center disk stem.