Percussion drilling apparatus

Claim 1

A PERCUSSION DRILLING TOOL COMPRISING (1) A HOLLOW CYLINDRICAL HOUSING, (2) AN ANVIL CONTAINING AN EXHAUST PASSAGEWAY, SAID ANVIL SLIDABLY CONSTRAINED WITHIN SAID HOUSING AND SO SHAPED RELATIVE THERETO THAT AXIAL TORQUE MAY BE TRANSMITTED THEREBETWEEN, SAID ANVIL PROTRUDING FROM SAID HOUSING AND INCLUDING COUPLING MEANS FOR ATTACHING A DRILL BIT, (3) A HOLLOW HAMMER ADJACENT SAID ANVIL, SLIDABLY CONSTRAINED WITHIN AND CLOSELY FITTING SAID HOUSING, SAID HAMMER BEING SHAPED TO DEFINE AN ANNULAR RECESS TN THE OUTER SURFACE THEREOF, (4) A HOLLOW FINGER VALVE SLIDABLY DISPOSED IN SAID HAMMER AND LONGER THAN SAID HAMMER BY APPROXIMATELY THE LENGTH OF STROKE OF SAID HAMMER, THE END ADJACENT SAID ANVIL BEING OF SHAPE AND ALIGNMENT TO SEAL SAID EXHAUST PASSAGEWAY, (5) MEANS WITHIN SAID HAMMER AND RESPONSIVE TO THE DIFFERENCE IN PRESSURE ON THE ENDS OF SAID HAMMER FOR MOVING SAID FINGER VALVE IN THE DIRECTION OF THE HAMMER END UNDER GREATER PRESSURE, (6) SAID HOUSING DEFINING A STATIONARY INLET FLUID PASSAGEWAY AND SEPARATE, STATIONARY UPPER AND LOWER FLUID CONDUITS, THE LATTER COMMUNICATING AT ALL TIMES RESPECTIVELY WITH THE UPPER AND LOWER ENDS OF SAID HAMMER, SAID UPPER AND LOWER CONDUITS TERMINATING ADJACENT SAID ANNULAR RECESS AND LONGITUDINALLY SEPARATED BY A DISTANCE APPROXIMATELY EQUAL TO THE WIDTH THEREOF, (7) AN ANNULAR SLIDE VALVE MOUNTED WITH LIMITED AXIAL MOVEMENT IN SAID HOUSING AND ABOUT SAID HAMMER AND CLOSELY FITTING SAID HOUSING AND SAID HAMMER, SAID VALVE BEING APPROXIMATELY THE SAME WIDTH AS THAT OF SAID ANNULAR RECESS, THE UPPER AND LOWER ENDS OF SAID SLIDE VALVE BEING IN CONSTANT FLUID COMMUNICATION WITH SAID UPPER AND LOWER FLUID CONDUITS RESPECTIVELY, SAID SLIDE VALVE BEING INTERPOSED BETWEEN SAID ANNULAR RECESS AND SAID UPPER AND LOWER FLUID CONDUITS BUT SO ARRANGED AS TO ADMIT FLUID CONTINUOUSLY FROM SAID INLET FLUID PASSAGEWAY TO SAID ANNULAR RECESS, SO THAT DIFFERENCES IN FLUID PRESSURE BETWEEN SAID UPPER AND LOWER CONDUITS CONTROLS THE AXIAL DISPLACEMENT OF SAID SLIDE VALVE IN SAID LIMITED AXIAL MOVEMENT AND THUS CONTROLS FLOW OF FLUID TO SAID UPPER AND LOWER FLUID CONDUITS, AND (8) A RECESSED UPPER HEAD FIXED TO SAID HOUSING ABOVE SAID HAMMER, THE RECESS IN SAID HEAD BEING SHAPED AND ALIGNED TO FIT CLOSELY THE UPPER END OF SAID FINGER VALVE WHEN SAID HAMMER IS NEAR THE TOP OF ITS STROKE.