Abstract: A vent check valve having a relatively flat configuration of its elements, being thereby adapted to utilize a local wall area of a housing to be vented as a supporting body and to provide a valve seat. The valve elements include an elastomeric flat diaphragm and a retainer for holding the diaphragm against the valve seat. These elements are disposed in respective counterbores formed in the wall body concentrically with the valve seat. The retainer has a spiderlike configuration with circumferential legs dimensioned to flex rearwardly in the associated counterbore upon installation to produce a self-locking wedge fit therein.