Valveless down-the-hole drill

A valveless percussive down-the-hole drill actuated by a supply of pressure fluid, comprising

• an outer wear sleeve,
• a backhead assembly secured to one end of the outer wear sleeve connectable to a drill string and to a supply of pressure fluid, through the drill string,
• a pressure fluid diverter located within the outer wear sleeve adjacent to the backhead,
• a drill bit suspendably supported in bit retaining means secured to the other end of the outer wear sleeve,
• an inner sleeve located inside the outer wear sleeve towards the said one end thereof adjacent to the pressure fluid diverter, defining a fluid passageway between the inner sleeve and the outer wear sleeve allowing fluid communication between the pressure fluid diverter and a chamber so defined within the outer wear sleeve and between the diverter at one end and the drill bit at the other end,
• a piston disposed within said chamber having a first slidable contact surface with a first chamber wall portion towards one end of the piston and a second slidable contact surface with a second chamber wall portion towards the other end of the piston so as to be slidably reciprocable within the said chamber,
• a porting means associated with the inner sleeve and the piston for alternately directing live pressure fluid from the said fluid passageway to either end surface of the piston so as to reciprocate the piston and to cause it to repeatedly strike the drill bit,
• an exhaust means operably associated with the porting means for alternately exhausting pressure fluid supplied to either side of the piston to the drill exterior and
• a means for trapping a volume of pressure fluid in a space defined intermediate said first and second sliding contact surfaces of the piston between the piston and the outer wear sleeve, such that when said volume is compressed during rearward motion of the piston the trapped pressure fluid firstly exerts a retarding force against the rearward motion of the piston and then exerts an additional driving force at the commencement of forward motion.