Patent ID: 8141663

Claim:
A down-hole drilling tool comprising: a housing; a bit connected to an end of the housing and adapted to drill rock; a piston comprising a central piston bore and at least one conduit communicating with the central piston bore; a control tube including at least one port, the control tube receiving a flow of motive fluid comprising an actuator supply portion and a bit flow portion; a drive chamber above the piston; and a return chamber between the piston and the bit; wherein the control tube extends through the central piston bore and the piston reciprocates along the control tube; wherein reciprocation of the piston along the control tube periodically places the at least one conduit in the piston in communication with the at least one port in the control tube; wherein periodic communication between the at least one conduit and at least one port causes the actuator supply portion of the motive fluid in the control tube to be supplied to the drive chamber and return chamber in alternating fashion, to cause the piston to respectively move into impact with the bit and lift away from the bit; wherein the actuator supply portion of the motive fluid becomes actuator exhaust upon flowing out of the drive chamber and return chamber, the actuator exhaust flowing along an actuator exhaust path and being vented above the bit; wherein the bit flow portion of the motive fluid in the control tube flows along a bit exhaust path and is vented through the bit; and wherein the bit exhaust path is separate from and schematically parallel to at least a portion of the actuator exhaust path.