Abstract: This invention relates to a cyclic hydraulic actuator, and more particularly to an actuator for a rock drill and includes: a housing; at least two chambers in the housing; a fluid passage between a first of the chambers and the outside of the housing for feeding a liquid at supply pressure to the chamber during operation of the actuator; a fluid passage between a second of the chambers and the outside of the housing for exhausting liquid from the second chamber during operation of the actuator; a piston reciprocable on an axis in at least the first and second chambers with the piston including an exposed piston area in each of the two chambers for causing, with the liquid at supply pressure, reciprocation of the piston; an inlet valve for opening and closing the second chamber to liquid at supply pressure in the first chamber; an exhaust valve for opening and closing the exhaust passage; the inlet and exhaust valves, chambers and exposed piston areas being so arranged that during cyclic operation of the actua