Hybrid hydraulic down-the-hole hammer

Abstract

The present invention relates to a closed-loop hydraulic down-the-hole hammer. The hammer comprises an elongate shaft and a piston having a central bore therethrough, the piston slidably mounted for reciprocal movement on the shaft and arranged to impact a percussion bit, wherein forward and rear drive chambers for the piston are disposed between the piston and the shaft and wherein the forward chamber is separated from the rear chamber by an annular shoulder formed internally of the piston bore. The hammer also comprises a control valve to control reciprocation of the piston, wherein the control valve is arranged within the central bore of the piston. The hammer further comprises an outer wear sleeve, wherein the piston is housed within the outer wear sleeve. A supplementary rear drive chamber is disposed internally of the outer wear sleeve. According to another aspect of the invention, the hammer comprises a control valve housing, disposed at least partially within the central bore of the shaft at a forward end of the shaft and arranged to receive the control valve, the control valve housing having a tapered outer surface at a forward portion thereof and an annular flange connected to the shaft and having a tapered inner surface, corresponding in shape to and engageable with the tapered outer surface of the control valve housing, whereby the control valve housing is retained in the shaft by the annular flange. The hammer further comprises engagement means on the control valve housing slidably engageable with complementary engagement means on the shaft to prevent relative rotation therebetween.