Abstract: A shut-off valve includes a valve housing having at least two mutually connecting chambers communicating with each other in each case via a passage opening bounded by a valve seat surface and provided with ports for feed and discharge of a medium. The shut-off valve includes a valve body which is provided with a closing surface co-acting with each valve seat surface for closing the associated passage opening and which is movable between a first position in which the closing surface is in sealing contact with the valve seat surface and a second position in which the closing surface is situated at a distance from the valve seat surface. Connecting onto either of the valve seat surface or the closing surface, at the position opposite which the other is situated close to the end of the movement from the second to the first position, is a slit-forming surface with at least one considerable axial directional component, and a plurality of notches is formed in the slit-forming surface.