A method for operating a valve comprising a first valve part having at least one opening (2, 5) formed therein and a second valve part having at least one opening (4, 6) formed therein, the first valve part and the second valve part are in the form of a substantially circular disk with relative movements being rotational, wherein at least one of the circular disks can rotate about an axis extending through the centre of each of the circular disks, the first and second valve parts being adapted to perform relative movements, the relative position of the opening(s) (2, 5) of the first valve part and the opening(s) (4, 6) of the second valve part defining an opening degree of the valve by means of an overlapping area of an opening (2, 5) of the first valve part and an opening (4, 6) of the second valve part, the method is characterized by: - moving the first valve part and/or the second valve part from a position defining a maximum opening degree of the valve towards a position defining a minimum opening degree of the valve in such a manner that the velocity of the relative movement between the first valve part and the second valve part varies as a function of an overlapping area between an opening (2, 5) of the first valve part and an opening (4, 6) of the second valve part, in such a manner that the velocity is decreased as the overlapping area decreases, and further comprising the step of increasing the relative velocity after the position defining a minimum opening degree has been reached until the valve parts (1, 2) reaches the next position where opening of the valve can be initiated, and wherein the step of moving the first valve part and/or the second valve part comprises the steps of the velocity being varied in a stepwise manner by - moving the first valve part and/or the second valve part at a first relative velocity, v 1, until a predefined overlapping area is reached, and subsequently moving the first valve part and/or the second valve part at a second relative velocity, v 2, until the overlapping area is zero, the valve thereby being in a closed position, wherein v 2 is significantly lower than v 1, and wherein the predefined overlapping area is within the interval from 40% to 80% of a maximum overlapping area. - moving the first valve part and/or the second valve part from a position defining a maximum opening degree of the valve towards a position defining a minimum opening degree of the valve in such a manner that the velocity of the relative movement between the first valve part and the second valve part varies as a function of an overlapping area between an opening (2, 5) of the first valve part and an opening (4, 6) of the second valve part, in such a manner that the velocity is decreased as the overlapping area decreases, and further comprising the step of increasing the relative velocity after the position defining a minimum opening degree has been reached until the valve parts (1, 2) reaches the next position where opening of the valve can be initiated, and - moving the first valve part and/or the second valve part at a first relative velocity, v 1, until a predefined overlapping area is reached, and subsequently moving the first valve part and/or the second valve part at a second relative velocity, v 2, until the overlapping area is zero, the valve thereby being in a closed position, wherein v 2 is significantly lower than v 1, and wherein the predefined overlapping area is within the interval from 40% to 80% of a maximum overlapping area.