Air or gas circulation rock bit anticontamination valve

Claim 1

A ROCK BIT HAVING A BODY ON WHICH CUTTERS ARE ROTATABLY MOUNTED, SAID BODY HAVING A MAIN CIRCULATION PASSAGE THERETHROUGH FOR THE DISCHARGE OF CIRCULATION FLUID, AND HAVING BRANCH PASSAGES EACH WITH A POINT OF COMMUNICATION WITH THE MAIN CIRCULATION PASSAGE AND LEADING TO THE INTERIORS OF THE CUTTERS, AN IMPERFORATE TUBULAR SLEEVE HAVING ITS LOWER END SNUGLY FITTING THE MAIN CIRCULATION PASSAGE BELOW THE POINTS OF COMMUNICATION OF THE BRANCH PASSAGES THEREWITH, SAID SLEEVE EXTENDING ABOVE SAID POINTS OF COMMUNICATION, THE WALL OF SAID MAIN CIRCULATION PASSAGE ADJACENT THE UPPER END OF SAID SLEEVE BEING SPACED OUTWARDLY FROM SAID SLEEVE TO PROVIDE CIRCULATION IN THE MAIN PASSAGE EXTERIORLY OF THE SLEEVE TO SAID POINTS COMMUNICATION WITH THE BRANCH PASSAGES AS WELL AS INTERIORLY OF THE SLEEVE, RELEASABLE SLEEVE ANCHORING MEANS ENGAGING THE WALL OF SAID PASSAGE AND SAID SLEEVE, AND A SUBSTITUTABLE DOWNWARDLY OPENING ONE-WAY VALVE SUPPORTED IN AND UPWARDLY REMOVABLE FROM SAID MAIN CIRCULATION PASSAGE AND HELD IN POSITION BENEATH AND BY SAID SLEEVE.