Butterfly valve seat construction

Claim 1

A BUTTERFLY VALVE, COMPRISING A CASING HAVING AN ANNULAR SEAT PORTION FORMED WITH A SEATING FACE; A DISC MEMBER PIVOTALLY MOUNTED IN SAID CASING; A ROTATABLE STEM IN TRUNNIONS WITHIN SAID CASING FOR ACTUATING SAID DISC MEMBER IN ITS PIVOTAL MOVEMENT RELATIVE TO SAID CASING; PIN MEANS MOUNTED BETWEEN SAID STEM AND DISC MEMBER TO RETAIN SAID LATTER MEMBERS IN RELATIVE NON-ROTATABLE RELATION; THE SAID DISC MEMBER HAVING RENEWABLE DEFORMABLE FLUID SEALING MEANS MOUNTED IN RECESSES OF SAID CLOSURE MEMBER AT END LIMITS OF SAID PIN MEANS; THE SAID RENEWABLE FLUID SEALING MEANS BEING OF A RESILIENT CONCAVE CONVEX CONSTRUCTION AND BEING FLUID PRESSURE RESPONSIVE WHEREBY TO EFFECT THE DEFORMATION OF SAID FLUID SEALING MEANS TO SNUGLY ENGAGE SIDE WALL PORTIONS OF SAID CLOSURE MEMBER DEFINING SAID RECESSES UPON THE APPLICATION OF LINE FLUID PRESSURE THERETO; SAID ANNULAR SEAT PORTION INCLUDING A PERIPHERAL OUTWARDLY FLANGED MEMBER WITH THE FLANGED PORTIONS THEREOF SPACED APART TO FORM THE END LIMITS OF THE SEATING FACE; THE INTERMEDIATE PORTION OF THE SEATING FACE BETWEEN SAID OUTWARDLY FLANGED PORTIONS PROVIDING FOR SAID SEATING FACE BEING OF A SPHERICAL DEPRESSION OF SUBSTANTIALLY CONSTANT WIDTH AND DEPTH TO FORM AN ANNULAR CONCAVE CONTACT FACE WITH THE PERIPHERY OF SAID DISC MEMBER EXCEPT FOR THAT PORTION FORMING THE CONNECTION WITH THE SAID STEM; THE SAID SEALING FACE UPON DETERMINED PIVOTAL MOVEMENT OF SAID DISC MEMBER CAUSING RADIALLY OUTWARD DISPLACEMENT OF SAID SEATING FACE TO FORM AN ANNULAR RECESSED CONTACT WITH THE PERIPHERY OF SAID DISC MEMBER SUBSTANTIALLY OF SPHERICAL ARCUATE CONFIGURATION WHEN VIEWED IN CROSS-SECTION.