Butterfly valve

A butterfly valve comprising:

• a valve body consisting of upper and lower halves and having an annular projection formed at an inner peripheral wall thereof for being accepted and held by an annular groove of a valve seat and further including annular end faces disposed so as to engage with corresponding faces of spaced apart conduits when installed therebetween;
• a valve seat having an annular groove into which the projection of said valve body is fitted, and including an external peripheral surface which fits to an internal peripheral surface of said valve body and further including a seat surface formed at an internal peripheral surface thereof;
• a rotatably supported valve stem passing through stem-inserting ports in said valve body and said valve seat, one end thereof protruding beyond the valve body;
• a disk-shaped valve member with a peripheral edge thinner than its central portion supported by the valve stem inside of the valve seat;
• annular sealing assemblies which are disposed in the interior of said stem-inserting ports of the valve seat and through which the valve stem is fitted to seal said ports around said valve stem, and
• a stem guide provided between said stem and said body for permitting the stem to rotate and for pressing said sealing assemblies in a radially inward direction of said valve;
• said valve seat comprising a first layer so formed as to have a substantially uniform thickness of hard synthetic resin and provided with said annular groove for fitting to the annular projection of the valve body, a second layer of resilient material covering the inner peripheral surface and either side surface of said first layer, and a third layer comprising a substantially uniform thin film of fluororesin,
• the inner peripheral portion of said second layer being sufficiently thick and resilient as to maintain the compression between the body and the valve disk in the closed position of the valve disk while the two side peripheral portions of the second layer, are less than half the thickness of the inner peripheral portion of the second layer so as to permit the space between said valve body and said conduits to be effectively sealed,
• said third layer being adhered to the inner peripheral surface and either side surface of the second layer and further extending into the inner peripheral surface of the stem-inserting ports at least to the second layer through which said valve stem is inserted, and further provided with an annular projection at the inner peripheral surface of stem-inserting ports of the third layer so as to press radially inwardly the valve stem for sealing a space between the valve seat and the valve stem,
• said seat surface of the valve seat comprising two side portions and a radially inwardly extending portion defined therebetween which presses radially inwardly the valve disk in the closed position,
• and said annular sealing assemblies comprising a resilient rubber ring and an O-ring of fluororesin disposed nearer to the valve member than the rubber ring.