A cementing valve for conducting cementing operations in a wellbore comprises a casing, wherein the cementing valve comprises an inner sliding sleeve which in a closed position covers a number of openings through an outer pipe surrounding the inner sliding sleeve, and in an open position uncovers said openings, the sliding sleeve comprising an actuating unit requiring a predetermined force to be actuated from both the closed position to the open position and vice versa, an engaging unit being arranged on the inside of the sliding sleeve for being engaged by a well running tool comprising corresponding gripping unit. The cementing valve comprises at least one shear pin designed in such a manner that a predetermined force is necessary to overcome the shear resistance of the shear pin, the sliding sleeve being arranged for moving further past the shear pin when the shear pin breaks until the actuating unit engage a groove.