The prior art to which the invention is directed includes the art of Butterfly Valvesbeing of a type in which a usually circular vane or disk is rotatable in the valve passage between an open and closed position. When in the closed position, a valve member engages a valve seat with which it cooperates to provide a seal against leakage of the fluid in the pressurized line intended to be controlled by the valve. It is essential in valves of this type that the seal should be effective on each occasion of valve closing for the life of the valve to continuously provide positive shut off of the fluid without frequent maintenance and servicing of the seat.

The present invention is concerned with a Butterfly Valves provided with a valve seat having three layers which is completely unaffected by temperature changes and is not subject to wearing conditions by the corrosive fluid.

It is an important object of the present invention to provide a BUTTERFLY VALVES in which the inner peripheral surface of a valve body is provided with an annular projection so as to conform to the outer peripheral surface of a valve seat having three layers, whereby said valve seat is tightly engaged with the inner peripheral surface of the valve body.

It is another object of the present invention to provide a butterfly valve in which a valve seat has three layers such as a first layer formed from hard synthetic resin, a second layer from resilient material and a third layer from fluororesin.

It is a further object of the present invention to provide a butterfly valve in which the second layer of a valve seat is so formed that its barrel portion is thick relative to the side peripheral portions contacting the two side surfaces of the first layer.

It is still another object of the present invention to provide a butterfly valve in which the third layer forming the inner and side peripheral surfaces of a valve seat extends to provide inner peripheral surfaces of stem-inserting ports.

It is still another object to provide a butterfly valve in which there are provided sealing assemblies each comprising a rubber ring and a seal ring made of fluororesin which is disposed nearer to the valve member than the rubber ring, in order to prevent leakage of the liquid between a valve seat and a valve stem, said seal ring comprising a O-ring or a ring of V-shaped section.

It is still another object of the present invention to provide a butterfly valve in which the inner peripheral surface of a valve seat is so formed to have a raised central portion, whereby a valve member in a closed position is resiliently urged at its peripheral edge by the raised portion of the seat.

It is a still further object of the present invention to provide a butterfly valve in which a port of a valve member through which a valve stem is passed is provided in its interior with a cylindrical core of metal, said valve member being formed from chemical resistant resin.

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