Abstract: In rock drilling utilizing mechanical destruction of the rock and circulation of drilling fluid for removing debris from the cutting face, the drilling fluid is directed on to the cutting face in the form of two opposed pulsed jets, the cycles of which are 180.degree. out of phase. In order to achieve the phased opposition of the pulsed jets a ball is disposed in the distribution chamber of the drilling fluid and is subjected to a combination of hydraulic and mechanical forces which cause the ball to oscillate between two end positions in which the ball respectively closes off one of two outlet ducts leading to nozzles which direct the drilling fluid towards opposite points on the bottom of the drill hole.