Hydraulic jarring tool

Claim 1

A JARRING TOOL CAPABLE OF BEING DROPPED DOWN THROUGH A DRILL STRING AND A DRILL COLLAR TO A POSITION IN CONTACT WITH A BIT SUPPORTED FROM THE LOWER END OF SAID COLLAR WHEN SAID DRILL STRING AND COLLAR ARE IN A BORE HOLE FILLED WITH A FLUID WITH SAID FLUID STANDING AS A COLUMN IN SAID DRILL PIPE AND COLLAR, INCLUDING: A TUBULAR SHELL HAVING AN UPPER PORT, A LOWER PORT, AND TWO OPPOSITELY DISPOSED TRANSVERSE BORES; A TUBULAR ANVIL SUPPORTED FROM THE LOWER END OF SAID SHELL, WITH SAID ANVIL RESTING ON SAID BIT SO AS TO TRANSMIT IMPACTS THERETO; A MANDREL SLIDABLY MOVABLE IN SAID SHELL; A SLEEVE EXTENDING UPWARDLY FROM SAID MANDREL BEYOND THE UPPER END OF SAID SHELL, SAID SLEEVE HAVING A FIRST PORT THEREIN THAT IS TRANSVERSELY ALIGNED WITH SAID UPPER PORT WHEN SAID SLEEVE AND MANDREL ARE IN A FIRST ELEVATED POSITION ABOVE SAID ANVIL; PRESSURESENSITIVE HOLDING MEANS CARRIED BY SAID MANDREL AND IN ALIGNMENT WITH SAID TRANSVERSE BORES IN SAID SHELL SO AST TO BE SUBJECTED TO THE PRESSURE OF SAID FLUID IN AN ANNULUS BETWEEN SID TOOL AND DRILL COLLAR, WITH SAID HOLDING MEANS MANTAINING SAID MANDREL AND SLEEVE IN SAID FIRST POSITION UNTIL SAID HOLDING MEANS IS SUBJECTED TO GREATER THAN A PREDETERMINED DOWNWARD FORCE THAT IS GENERATED BY PUMPING SAID FLUID INTO SAID DRILL PIPE AND DRILL COLLAR DOWNWARDLY THROUGH SAID SHELL, OUTWARDLY THROUGH SAID UPPER PORT TO DEVELOP A BACK PRESSURE IN SAID SHELL GREATER THAN SAID PREDETERMINED DOWNWARD FORCE, WITH SAID FLUID AS DISCHARGED FROM SAID UPPER PORT ENTERING SAID ANNULUS WHICH FLUID FLOWS FROM SAID ANNULUS THROUGH SAID LOWER PORT ITO SAID SHELL TO ENTER A PASSAGE FORMED IN SAID BIT THAT EXTENDS THERETHROUGH TO COMMUNICATE WITH SAID FLUID IN A SECOND ANNULUS-SHAPED SPACE DEFINED BETWEEN SAID BORE HOLE AND THE EXTERIOR SURFACES OF SAID DRILL COLLAR AND SAID DRILL PIPE; MEANS FOR MAINTAINING SAID MANDREL AND SLEEVE IN A NON-ROTATING POSITION IN SAID TUBULAR SHELL; AND SPRING MEANS FOR RETURNING SAID MANDREL AND SLEEVE TO SAID FIRST POSITION AFTER SAID BACK PRESSURE HAS FORCED SAID MANDREL AND SLEEVE DOWNWARDLY FROM SAID FIRST POSITION TO A SECOND POSITION WHERE SAID MANDREL IMPACTS SAID ANVIL AND IMPARTS A JAR TO SAID BIT.