Abstract: A passive exhaust valve assembly includes an exhaust conduit that has a first pipe section attached in generally axial alignment with a second pipe section. The end portion of the first pipe section includes a circumferential segment disposed within the end portion of the second pipe section to form an overlapping interface. The end portions of the first and second pipe sections each include a flange protruding radially outward from the respective first or second pipe section, whereby the flanges engage with each other to form an axle seat therebetween. A support shaft extends laterally across an interior volume of the exhaust conduit and rotatably engages the axle seat. A valve plate is coupled to the support shaft within the interior volume of the exhaust conduit for moving relative to the exhaust conduit between open and closed positions.

Abstract: The present invention is directed to a unit for eliminating offensive odors. An electrostatic filter assembly embodiment of the present invention includes a casing, a substantially sheer electrostatic filter sheet, and a substantially silent blower. A filtered animal litter box embodiment of the present invention includes an enclosure, a filter assembly, a conduit, a filter cartridge, and a substantially silent blower. A kit of parts having components of the filtered animal box is also contemplated.