Valve having a seat cleaning feature

Claim 1

IN A VALVE HAVING A BODY PORTION WITH A MAIN BORE AND HAVING A MOVABLE VALVE MEMBER WITH AN ENLARGED DISC PORTION, SAID BODY HAVING A COUNTER-BORE OUTWARDLY OF THE BODY FROM THE MAIN BORE ADAPTED TO RECEIVE SAID DISC PORTION, AN ANNULAR TAPERED SHOULDER BETWEEN SAID MAIN BORE AND COUNTER-BORE TAPERING IN THE DIRECTION OF FLOW THROUGH THE VALVE, THE DISC PORTION OF THE VALVE MEMBER HAVING AN ANNULAR TAPERED PORTION FOR COACTION WITH SAID ANNULAR TAPERED SHOULDER, AT LEAST THE INNER ANNULAR PORTION OF SAID TAPERED SHOULDER FORMING AN ANNULAR VALVE SEAT AND THERE BEING AN ANNULAR PURGE CHAMBER UPSTREAM OF THE SEAT TAPERED IN THE GENERAL DIRECTION OF SAID SEAT, THERE BEING DUCTS IN THE BODY PORTION EXTENDING FROM THE EXTERIOR INTO SAID PURGE CHAMBER AND HAVING DISCHARGE PORTIONS INCLINED IN A DIRECTION TO DISCHARGE IN THE DIRECTION OF TAPER OF SAID SHOULDER TOWARD THE VALVE SEAT WHEREBY A PRESSURIZED PURGING AGENT IN SAID DUCTS WILL BE DIRECTED INTO SAID PURGE CHAMBER TO KEEP THE LATTER FILLED WITH A PURGING AGENT FOR CONSTANT DISCHARGE ACROSS ALL PORTIONS OF THE PERIPHERY OF SAID VALVE SEAT PORTION OF THE SHOULDER AND IN THE GENERAL DIRECTION OF FLOW THROUGH THE VALVE.