Abstract: The invention relates to a rotary slide valve, the cylindrical valve member of which is mounted with its axis of rotation transverse to the flow and rests within a fixed coaxial cylinder of approximately the same size, of which the orifices allowing the flow medium to pass through are controlled by orifices and wall parts of the valve member. The valve member is surrounded coaxially by an outer cylinder which has a larger diameter and which possesses on each of its sides located opposite one another respectively an inlet and an outlet and first and second conduits, so that, in the normal position of the valve member, the inlet on the one side is connected to the second conduit on the other side and the outlet on the one side is connected to the first conduit on the other side and, in the deflected position, the inlet and first conduit are connected to one another and the outlet and second conduit are connected to one another.