Lubricated ball plug valve with relieved surface on seat ring

Claim 1

A PLUG VALVE COMPRISING: A BODY HAVING INLET AND OUTLET PASSAGES; A PORTED PLUG IN SAID BODY HAVING SPHERICAL SEATING SURFACES; CONCAVE SURFACED SEATS WITHIN SAID BODY AT OPPOSITE SIDES OF SAID PLUG AND AT RESPECTIVE INNER ENDS OF SAID INLET AND OUTLET PASSAGES WITH AT LEAST A PORTION OF THE CONCAVE SURFACE OF EACH SEAT SUPPORTING SAID PLUG ON ITS SPHERICAL SEATING SURFACES AND ENABLING TURNING MOVEMENT OF SAID PLUG BETWEEN VALVE OPEN AND VALVE CLOSED POSITIONS; SAID SEATS BEING RIGID AND SUBSTANTIALLY NON-DEFORMABLE UNDER VALVE OPERATING PRESSURES; SAID PLUG SPHERICAL SEATING SURFACE ENGAGING A CIRCULAR PORTION OF AT LEAST THE DOWNSTREAM SEAT CONCAVE SURFACE WHICH IS SITUATED OUTWARD IN A RADIAL SENSE FROM THE MAJOR PORTION OF SAID ASSOCIATED CONCAVE SEAT SURFACE AND, WHEN THERE IS NO DROP IN PRESSURE ACROSS THE PLUG, BEING SEPARATED FROM THE CONCAVE SEAT SURFACE OVER A SUBSTANTIAL ANNULAR AREA EXTENDING OUTWARDLY IN A RADIAL SENSE FROM AND INCLUDING THE INNER PERIPHERY OF THE CONCAVE SEAT SURFACE.