Abstract: A control valves for a servo steering system, having an inlet for supplying a hydraulic liquid at a first pressures and an outlet for discharging the hydraulic liquid into a region having a smaller, second pressure, especially into a pressureless reservoir. The control valve has a guide and a valve slide accommodated in the guide so as to be movable therein along an axis. The valve slide is acted upon on one side by the hydraulic liquid with the first pressure and on the opposite side by a defined supporting force. An opening structure is provided on at least one of the valve slide and guide. A cover corresponding to the opening structure is provided on the other of the guide and valve slide. A movement of the valve slide relative to the guide effects a change of a free passage area of the opening structure that is not closed off by the cover, whereby the hydraulic liquid is able to flow from the inlet, through the free passage area, to the outlet.