A PERCUSSIVE DOWNHOLE HAMMER AND PISTON DESIGN FOR SUCH A HAMMER

摘要

This invention relates to a piston (10) for use in a downhole percussive hammer where the piston (10) comprises a first section (11) and a second section (12) at the forward end of the piston where the diameter of the seco nd section (12) is smaller than that of the first section (11). An axial hole (13) extends through the length of the piston (10). At least one first condu it (15) extends from the upper end (16) of the piston (10) to a position intermediate the ends of the first section (11). At least one external secon d conduit (20) formed in the outer surface of the first section (11) extends between but not to the upper and lower ends (16 and 17) of the first section (11). Conduits (18 and 21) extend from the lower end of the first conduit (1 5) and the upper end of the second conduit (20) through the first section (11) to the axial hole (13). The invention provides significant advantages including maintaining high pressure air in the conduits (20 and 21) after and before a ir flow through them.