Patent ID: 6499544
Filing Date: 2002-12-31
Classification: E21B

Abstract:
A down-the-hole percussive hammer for rock drilling, comprising:a generally cylindrical casing defining a longitudinal center axis; a drill bit disposed at a front end of the casing; a piston mounted longitudinally behind the drill bit in the casing for reciprocation in a longitudinal direction for applying an impact to the drill bit during each forward stroke of the piston; a top sub mounted in a rear portion of the casing and including a central passage for supplying operating air for reciprocating the piston, the central passage including a chamber disposed between front and rear ends of the top sub; a hollow feed tube mounted within the central passage and including a segment disposed within the chamber, the segment including longitudinally spaced air outlet and re-entry ports communicating with the chamber, the outlet port disposed rearwardly of the re-entry port; a seal disposed within the feed tube for sealing an interior of the feed tube between the outlet and re-entry ports, the seal being mounted against longitudinal movement relative to the feed tube; and a check valve for permitting a forward flow of operating air and preventing a rearward flow of fluid, the valve including an elastically resilient sleeve extending around an outer circumference of the feed tube for blocking the outlet port from the chamber, the sleeve being elastically expandible away from the outlet port by pressurized operating air to open the outlet port and permit operating air to flow out of the outlet port and into the chamber and then into the re-entry port.