Impact drilling tool

Claim 1

PERCUSSION DRILLING APPARATUS COMPRISING CYLINDRICAL WALL STRUCTURE FORMING A WORKING CHAMBER, A CONNECTION FOR OPERATIONG FLUID AT ONE END OF SAID CHAMBER, AN ANVIL SLIDABLY RECEIVED IN THE OPPOSITE END OF SAID CHAMBER, AN EXHAUST DUCT IN SAID ANVIL, A HAMMER PISTON RECIPROCABLE IN SAID CHAMBER AND FORMING PRESSURE CHAMBERS AT OPPOSITE ENDS THEREOF, A MAIN PRESSURE PORT AND SPACED EXHAUST PORTS IN SAID WALL STRUCTURE, PASSAGING IN SAID WALL STRUCTURE CONNECTING SAID PRESSURE PORT WITH SAID OPERATING FLUID CONNECTION AND ALSO CONNECTING SAID EXHAUST PORTS WITH SAID EXHAUST DUCT, SAID PISTON DURING BEING POSITIONED TO BE CONTROLLED BY SAID PISTON DURING NORMAL ON-BOTTOM OPERATION OF THE APPARATUS TO ALTERNATELY EXHAUST SAID PRESSURE CHAMBERS THROUGH SAID DUCT, SHUTTLE RECESS MEANS IN SAID PISTON AND SAID WALL STRUCTURE POSITIONED TO ALTERNATELY CONNECT SAID PRESSURE PORT WITH SAID OPPOSITE PRESSURE CHAMBERS, SAID PISTON BEING SHIFTABLE ABNORMALLY WHEN THE APPARATUS IS SUSPENDED OFF BOTTOM AND ONE OF SAID EXHAUST PORTS BEING POSITIONED TO COMMUNICATE DIRECTLY WITH SAID RECESS MEANS IN SAID PISTON DURING SUCH ABNORMAL SHIFTING OF SAID PISTON TO CAUSE THE OPERATION FLUID TO BYPASS SAID WORKING CHAMBER AND FLOW DIRECTLY INTO SAID EXHAUST PASSAGE AND SAID DUCT.