A down the hole drilling assembly having an elongate casing, a fluid powered piston, top and bottom working chambers, a plurality of fluid passages and an exhaust system, wherein the sum of the top work area and a top intermediate work area of the piston is equal to the cross-sectional area of the casing bore.

A down the hole drilling assembly having an elongate casing, a fluid powered piston, top and bottom working chambers, a plurality of fluid passages and an exhaust system, wherein the sum of the top work area and a top intermediate work area of the piston is equal to the cross-sectional area of the casing bore.

A down the hole drilling assembly having a drill tube adapter, an elongate casing, a fluid powered piston, a top working chamber, a bottom working chamber, a top sub and an exhaust system, wherein the exhaust system is moveable with respect to the drill string. The top sub includes an exhaust valve arranged for opening and closing the connection between the at least one exhaust passage and the at least one exhaust port.

A down the hole drilling assembly having a drill tube adapter, an elongate casing, a fluid powered piston, a top working chamber, a bottom working chamber, a top sub and an exhaust system, wherein the exhaust system is moveable with respect to the drill string. The top sub includes an exhaust valve arranged for opening and closing the connection between the at least one exhaust passage and the at least one exhaust port.

A down the hole drilling assembly having an elongate casing, a fluid powered piston, top and bottom working chambers, a plurality of fluid passages and an exhaust system, wherein the sum of the top work area and a top intermediate work area of the piston is equal to the cross-sectional area of the casing bore.

A down the hole drilling assembly having an elongate casing, a fluid powered piston, top and bottom working chambers, a plurality of fluid passages and an exhaust system, wherein the sum of the top work area and a top intermediate work area of the piston is equal to the cross-sectional area of the casing bore.

A down the hole drilling assembly having a drill tube adapter, an elongate casing, a fluid powered piston, a top working chamber, a bottom working chamber, a top sub and an exhaust system, wherein the exhaust system is moveable with respect to the drill string. The top sub includes an exhaust valve arranged for opening and closing the connection between the at least one exhaust passage and the at least one exhaust port.

A down the hole drilling assembly having a drill tube adapter, an elongate casing, a fluid powered piston, a top working chamber, a bottom working chamber, a top sub and an exhaust system, wherein the exhaust system is moveable with respect to the drill string. The top sub includes an exhaust valve arranged for opening and closing the connection between the at least one exhaust passage and the at least one exhaust port.