Abstract: A butterfly valve including a housing having a hollow passage defining a flow path and a shaft mounted to the housing and extending transversely across the flow path. The shaft defines an axis of rotation for a butterfly valve element carried on the shaft. The valve element can be rotated about the axis between an open position permitting flow along the flow path and a closed position restricting flow along the flow path. The butterfly valve element includes a thin, substantially disc-shaped, flow-regulating plate having front and rear faces and a flow-straightening vane extending from one of the faces transversely relative to the shaft. The vane is solid and extends substantially to the wall of the hollow passage thereby defining separate non-communicating flow channels on opposite sides thereof for reducing flow turbulence and for straightening and accelerating flow across the plate.