Abstract: A reverse circulation down-the-hole hammer drill apparatus for drilling rock and overburden comprises a fluid-driven piston which reciprocates in an annular chamber to repeatedly strike a bit suspended at one end of the chamber, for example in a splined mounting. Fluid is exhausted through the bit directly to the face of the bit and cuttings and debris are returned via a central throughbore in the bit and in the drill apparatus to the surface. The bit drops forward on encountering a void during drilling operations to open by-pass passages which exhaust fluid directly into the throughbore temporarily so as to prevent any loss of return of sample to the surface.

Abstract: A valveless down-the-hole hammer drill is actuated by fluid such as compressed air. The drill includes a piston disposed within a chamber defined within an outer wear sleeve, an air diverter at one end and a suspendably mounted drill bit at the other end, wherein the piston has a slidable contact surface with the chamber towards each end of the piston, such that the piston is slidably reciprocable within the chamber. Porting and exhaust arrangements alternately supply and exhaust live pressure fluid to either end surface of the piston to reciprocate it and cause it to repeatedly strike the drill bit. An intermediate compression chamber is defined between the two sliding contact surfaces of the piston between the piston and the outer wear sleeve. Air trapped in the intermediate chamber is compressed so as to apply a retarding force on the piston towards the end of the return stroke, and to provide additional impetus to the piston on the commencement of the drive stroke.