Fluid operated drill apparatus

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