<p>The surface (3) of the valve seat (2) is so inclined all-round that the points of intersection of diametrically opposed tangents (5-10) on the seat surface enclose a surface. The all-round seat surface (3) runs at right-angles to the verticals of the through flow direction. The angle of inclination of the seat surface over the complete periphery is of equal size to the verticals to the through flow direction. Also, over at least a part of the periphery, the inclination angle of the seat surface can be different to the verticals to the through flow direction. On the closure piece, a spindle is connected off-centre according to the inclined position of the valve seat (2).</p>
