ROCK DRILL

A rock drill including a first control valve (80), a first fluid circuit (70) suppliable with fluid via the first control valve (80), an impact piston (66) driveable by fluid pressure in the first fluid circuit, a plurality of first fluid circuit feedback paths (72) from the impact piston (66) to the control valve (80), a damping body (50) for damping backpressure from a rock face, a damping fluid chamber (52), associated with the damping body (50), characterised in a second fluid circuit (56) in fluid communication with the damping fluid chamber (52) and a stroke length control mechanism (91) actuable by fluid pressure in the second fluid circuit (56), wherein flow of fluid in said first fluid circuit feedback paths (72) is controllable by the stroke length control mechanism (91), whereby the driveable stroke length of said impact piston 66 may be adjusted.