The main object of the present invention is to provide a BUTTERFLY VALVES having good sealing capacity and not implying soft sealing element made of rubber, plastic or similar materials. More specifically an object is to produce a valve having good sealing capacity and which can be entirely manufactured of metal. An object of the present invention is, however, that the principles of the invention shall not exclude the use of such soft materials as e.g. PTFE and nylon. Butterfly ValvesThere is rather an object that such materials will also have to be used, e.g. in valve seats, if for some reason or other these are more suitable or otherwise more desirable than metallic materials. In other words, a purpose of the present invention is to create liberty of choice between different materials in regard to their convenience for the medium which the valve is intended to operate with.

Another object is to provide a valve the throttle of which when being turned from its shut-off to its open position and vice versa is not principally in contact with the valve seat, which is favourable from a wear point of view.

An object of this invention is also to provide a butterfly valve being sturdy and reliable, simple to operate and having a long life.

This invention is an improvement over the valve which is disclosed in SE No. 78 11864-3, which is characterized in that the seal face of the swivel throttle has two opposite, essentially spherical sections intersected by a symmetry plane through the throttle, which plane coincides with the swivel stem of the throttle and two opposite, essentially conically shaped sections on both sides of the aforementioned symmetry plane between the two essentially spherically shaped sections, and by the fact that the essentially spherically and the essentially conically shaped sections successively merge into each other.

Moreover, according to the invention, the center axis of the conically shaped faces is placed at a slight angle to a shaft coinciding with the above-mentioned symmetry plane and is perpendicular to the pivot shaft of the damper. The angle will vary according to the dimensions of the throttle, like its diameter and the width of the seal face. In the normal case the angle should be between 5° and 8°. At the same time it is suitable that the angle between the conical sections, i.e. the top rake of the cone, amounts to between 10° and 40°, at which the optimal angle is determined by the dimensions of the valve. The torsional axis of the valve further preferably is eccentrically journaled such that during the shutting movement there will be a combination of rotational and axial movements of the sealing line of the valve disc against the valve seat, said sealing line and valve seat both having circular shape and the same diameter.

According to the invention the seat further is arranged to be flexible and/or displaceable in its plane so that, when the valve disc is pressed against the seat, the seat can concur with the shape of the curve going around the circumference of the seal face at the level determined by the contact points between seal face and valve seat. According to the invention the curve mentioned before is circular. This implies that the seat is flexible and/or displaceable in its own plane so that it can adapt itself to the position of the throttle or valve disc when the valve is shut.Butterfly Valves More particularly the valve seat is suitably arranged displaceable in an annular groove in the valve housing. According to the best mode of carrying out the invention the annular groove is formed by a couple of spring washers which are for sealing reasons pressed to both sides of the valve seat ring. Suitably the spring forces of the spring washers are so great that the position of the seat ring will be maintained when the valve is reopened.

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