Abstract: A streamlined cylindrical flapper check valve is provided for use in fluid handling pipelines where corrosive products are being pumped. A cylindrical metal sleeve surrounds two cylindrical thermoplastic or thermoset elements, an upstream element having a throughhole of the same diameter as the pipeline and a downstream element with a throughhole larger than the pipeline diameter. A rotatable thermoplastic or thermoset flapper is mounted to the downstream element and rotates into a cavity in the downstream element to permit the full-flow passage of the product. The interface at which the two elements are in contact is inclined to the centerline axis of the central passage of the valve to permit the flapper, in the absense of flow in the line, to contact the sealing surface of the upstream element before the flapper becomes perpendicular to the center-line axis.