Abstract: Valve which consists of a body (1) provided with a flow passage, of a closing member (2), such as, e.g., a flap, fitted in the flow passage (3) pivotably or turnably and having no passage opening, and, if necessary, of jointly operative sealing members (6) fitted between the closing member (2) and the valve body (1). In the flow passage (3) in the valve body (1), after the closing member (2), at the outlet side of the flow, one or several attenuation member or members (9) are fitted, which are placed one after the other at a distance from each other and from the closing member (2), which the closing member is in the closed position, and which reduce the cross-sectional area of the flow passage (3). The attenuation member or members (9) may be provided with holes or openings (12) passing through them.