Abstract: The present invention is directed to a multi-cuspid back-flow preventer in the nature of a check valve that has a generally annular body portion with axially spaced upstream and downstream ends. A substantially cylindrical passageway extends through the body portion, and a plurality of circumferentially adjacent valve cuspids are connected to the downstream end of the body portion for selectively opening and closing the passageway that extends therethrough. Each valve cuspid is marginated by a rib that extends into the passageway. Breather slots are provided between the successively adjacent valve cuspids, and a mounting flange may be provided at the upstream end of the body portion.