PERCUSSIVE DOWN-THE-HOLE HAMMER FOR ROCK DRILLING, A TOP SUBUSED THEREIN AND A METHOD FOR ADJUSTING AIR PRESSURE

摘要

A down-the-hole percussive hammer includes a cylindrical casing adapted to carry a drill bit, and a piston mounted in the casing for reciprocal movemen t to repeatedly strike the drill bit. A top sub is mounted at a rear portion o f the casing, the top sub including a front face facing the piston. A feed tub e is mounted to the top sub and extends forwardly along a center axis of the casing and defines an air-conducting passage. The piston includes an axial through-hole which slidably receives the feed tube. The front face and the feed tube together define a recess opening toward the piston. A removable volume-changer is insertable into the recess to vary a volume of a space in which the piston slides, and thus control a pressure at which the piston operates.