An air admittance valve for a plumbing drainage system includes a housing defining an interior space and having an air inlet for admitting air into the interior space. The housing is adapted to be connected to a plumbing drainage system, such that the interior space is in fluid communication with the plumbing drainage system.
The air admittance valve also includes an air pressure actuated seal element for selectively sealing the air inlet and guide means for guiding the seal element into engagement with the air inlet. The guide means is arranged, in normal use, below the seal element.