Abstract: A check valve particularly for use in large-volume applications includes a self-contained pressing unit which is mounted on a common pivot with the valve member in the outlet compartment of the valve housing and presses the valve member towards its closing position in which it sealingly contacts the valve seat. The pressing unit includes an elongated support member and an L-shaped pressing member which are mounted on a bearing sleeve for angular displacement relative to one another about the axis of the bearing sleeve. A buckling-type spring is mounted between a free end portion of the support element and the region of merger of the two legs of the L-shaped pressing member, the spring urging the pressing component away from the support component, and against the valve member upon installation on the pivot. The spring characteristic is such that the spring force initially rapidly increases, than drops precipitously and then remains substantially constant over a substantial range of deformation of the spring.