Patent ID: 7875172

Claim:
A back-water trap unit comprising: (i) a housing having (a) a base with an upper surface; (b) an outer perimetric housing wall having an inner surface, an outer surface, and upper and lower wall edges and being sealingly connected at the lower wall edge to the upper surface of the base to define an enclosure; and (c) a housing cover removably securable to the upper wall edge and comprising a plurality of inlet apertures; (ii) an interior wall having (a) an upper interior wall edge; (b) a lower interior wall edge sealingly connected to the upper surface of the base to define an inner compartment and an outer compartment within the enclosure, the interior wall having a height less than a height of the housing wall; (c) an inner compartment cover sealingly connected to the upper interior wall edge and to the inner surface of the housing wall; (d) an inlet aperture proximate the lower interior wall edge and having an upper edge; and (e) a flapper valve pivotally secured to the interior wall within the inner compartment, constructed and arranged to rotate between an inlet open position and an inlet closed position in response to liquid pressure from the enclosure; and (iii) an outlet through the housing wall constructed and arranged to provide a fluid discharge conduit from the inner compartment, and located at a vertical height at least equal to the vertical height of the upper edge of the inlet aperture above the upper surface of the base.