Abstract: A bidirectional fluid flow control valve has two bifurcated elastic seat rings positioned in respective undercut grooves which are spaced apart in the flow passageway of the valve body, one on either side of the axis of rotation of a butterfly valve disc having two corresponding spaced apart annular sealing surfaces. One of the undercut seat grooves may be formed in a separate detachable seal ring to facilitate assembly of the disc in the valve. The valve disc is axially symmetrical with respect to its midplane, so that operating torque and flow characteristics of the valve are the same regardless of the direction of fluid flow through the valve.