Abstract: Down-the-hole drill comprising a housing (1), a hammer piston (6) movable to-and-fro in the housing and intended for impacting a drill bit (5). A back piece (3) provided with an extension (12) with a valve part (17) cooperates with a part (8) of a central channel in the hammer piston. This part of the central channel comprises a zone (16) with larger diameter than adjacent parts at an intermediate part of this part. This results in that pressure medium can pass the valve part when it is situated at the zone and that the valve part and the hammer piston sealingly cooperate when the valve part is on either side of the zone.

Abstract: Down-the-hole drilling machine comprising a housing in form of a tube (1), a hammer piston (6) being movable to-and-fro in the tube and intended for impacting a drill bit (5). The hammer piston is at its ends provided with end sections in form of polygons with rounded corners (51, 52). These end sections are turned relative to each other an angle which is half as large as the angle between two adjacent corners.