Down the hole drilling assembly exhaust assembly

A down the hole drilling assembly having a top end arranged for coupling to a drill string and a bottom cutting end, the drilling assembly comprising:

• a drill tube adapter positioned at the top end of the assembly;
• an elongate casing;
• a drill bit at least partially accommodated within the bottom end of the casing;
• a fluid powered piston arranged moveably inside the casing to shuttle axially back and forth;
• a top working chamber at a top end side of the piston;
• a bottom working chamber at a bottom end side of the piston;
• a top sub including a retaining shoulder, a plurality of splines, at least one exhaust passage engaged with the casing, wherein the at least one exhaust passage is connected to the top chamber via at least one top vent passage;
• at least one flushing port at the bottom end of the casing and being connected to the at least one bottom vent passage arranged to vent the bottom chamber;
• and
• an exhaust system at the top end of the casing including an exhaust cover and at least one exhaust port arranged to vent the top chamber via the at least one exhaust passage, wherein the exhaust system is moveable with respect to the drill string and 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.