Patent ID: 7353890
Filing Date: 2008-04-08
Classification: E21B

Abstract:
1. A down-the-hole hammer, comprising: a casing; a piston movable in the casing between a lowermost operating position and an uppermost operating position, a recess being provided between the piston and the casing so that the piston and the casing define an intermediate chamber between a top end of the piston and a bottom end of the piston; and a passageway between a source of pressurized fluid and the intermediate chamber such that, at all positions of the piston between the lowermost and the uppermost operating positions, the source of pressurized fluid is in flow communication with the intermediate chamber through the passageway, an opening in the piston at least partially defining the passageway, wherein the casing includes a top internal recess that permits direct flow communication between the intermediate chamber and a top chamber defined by the top end of the piston and the casing when the piston is in the uppermost operating position.