Butterfly valve

The flap valve comprises a housing (1) with a rotatably installed shut-off flap (5) which is connected to an operating element located outside the housing via a rotation transmission component guided through an opening in one wall of the housing. A seal is provided for the sealing of the inside of the housing and by especially a spring is pressed against the housing and/or against the rotation transmission component. Means are also provided by which the seal during rotation of the shut-off flap is at least partially rotated along with it.