The present invention is a one piece sleeve for a rotary valve, the sleeve comprising an array of communication slots formed in the bore of the sleeve, characterized in that at least a portion of the floor of one of said slots is convex. Figure depicts sleeve (1b) with arcuate slot (21b) which has a convex floor and is open ended at both axial extremities of surface (17b) of bore (16b) of sleeve (1b). This slot may preferably be used as a return slot on the sleeve.