Abstract: A valve assembly is disclosed for use within a flow path for permitting relatively free flow in said flow path in a first direction and for preventing flow in said path in a second, opposite direction. The assembly includes a resilient flow regulator including a pair of lips arranged in a converging relationship to define a normally closed slit at the outer ends of the lips. An annular flange extends outwardly about the opposite end of the regulator. A housing outlet portion defines a housing interior approximating the shape of the regulator, having a pair of planar surfaces corresponding to the pair of lips. The housing outlet portion further includes an annular collar disposed outwardly adjacent the base of each planar surface. The regulator is disposed within the housing outlet portion with the flange contained within the collar, with the lips being adjacent to but not in contact with the planar surfaces. A cover plate is attached to the collar for securing the regulator and for sealing the housing.