Abstract: A bottom hole assembly (BHA) and method for drilling a bore with a pneumatic percussion hammer includes an expandable packer surrounding the stem rod connected to the hammer. The packer has an inner surface confronting the outer surface of the stem rod in an axially slideable, sealed relationship. The packer is expanded and fixed in the bore to separate a region of high hydraulic pressure above the packer from a region of lower hydraulic pressure below the packer. The method includes operating the pneumatic hammer and bit, while (i) the stem rod advances with a sliding seal against an inside surface of the expanded packer; (ii) pneumatic pressurization and exhaust for the hammer are guided within the stem rod; and (iii) the exhaust from the hammer is discharged into the lower clearance region surrounding the bit at the bottom of the bore.

Abstract: A bottom hole assembly (BHA) and method for drilling a bore with a pneumatic percussion hammer includes an expandable packer surrounding the stem rod connected to the hammer. The packer has an inner surface confronting the outer surface of the stem rod in an axially slideable, sealed relationship. The packer is expanded and fixed in the bore to separate a region of high hydraulic pressure above the packer from a region of lower hydraulic pressure below the packer. The method includes operating the pneumatic hammer and bit, while (i) the stem rod advances with a sliding seal against an inside surface of the expanded packer; (ii) pneumatic pressurization and exhaust for the hammer are guided within the stem rod; and (iii) the exhaust from the hammer is discharged into the lower clearance region surrounding the bit at the bottom of the bore.

Abstract: A sleeve carried by and preferably slidable relative to the piston, for controlling air passages associated with a central air feed tube, whereby retraction pressure is applied to the piston substantially at impact. It is the impact itself of the piston against the bit, which enhances sliding of the sleeve relative to the piston, over the feed tube, and thereby switches the airflow at the moment of impact.