Ventilators

A canopy for use with a ventilator slot, the canopy comprising:

• an elongated housing having an interior, a bottom wall having an aperture to provide an inlet to the interior of the housing, imperforate front and top walls, a rear aperture to provide an outlet from said interior so as to provide a flow path for air through said interior from said inlet to said outlet, a longitudinal wall extending across said flow path, the longitudinal wall having an upstream side and a downstream side and containing a first set of apertures spaced longitudinally along said longitudinal wall, and at least one resilient baffle strip secured at a point of anchorage proximate an end thereof to the upstream side of said longitudinal wall, said resilient baffle strip extending away from said point of anchorage as a cantilever, the resilient baffle strip having a second set of apertures spaced longitudinally along said baffle strip, the second set of apertures being at least partially out of alignment with the first set of apertures;
• said longitudinal wall and said baffle strip being configured wherein, in the absence of a differential air pressure between said inlet and said outlet, said baffle strip being biased by its resiliency to a first position where the baffle strip diverges away from said longitudinal wall progressively more from said point of anchorage and, while in the presence of an increasing positive differential air pressure between said inlet and said outlet, said baffle strip moves progressively toward said longitudinal wall to a second position which partially obturates said first set of apertures.