Valve

A valve assembly for use with a vertical plumbing fluid conduit, and operative to vent the conduit responsive to a predetermined differential pressure between the interior of the conduit and outside atmosphere, comprising:

• a housing adapted for connection to an upper end of the conduit, the housing having a first flat vertical wall defining a valve plate with a fluid passageway therethrough;
• an elastomeric closure member with a resilient domed diaphragm, and an elongated resilient stem extending from the diaphragm and secured to the plate, the diaphragm having a convex side facing away from the plate, and a concave side facing the plate and having a perimeter in contact with the plate to close the passageway, the stem being stressed to urge the diaphragm perimeter against the plate, the diaphragm being resiliently flexed away from the plate to open the passageway when fluid pressure against the concave side exceeds fluid pressure against the convex side by a predetermined amount;
• and
• a cap fitted over the housing, the cap having a sidewall spaced from and extending downwardly over an outer surface of the housing to an open lower end to define a vent path from the valve plate downwardly to the open lower end.