The seal is for used with a shaft passing through the wall of an open or closed vessel, and comprises a disc fixed to the shaft and running parallel to and clear of the wall through which the shaft extends. Without causing any friction, this disc generates centrifugal currents preventing any fluid from escaping. The disc can have teeth, blades for mixing or shredding the material in the vessel, also circular or spiral grooves in the underside. A vaned wheel can also be fitted to the shaft between the disc and the vessel wall, or the disc can be pressed against the wall by a spring. Fluid or gas can be delivered by a nozzel from outside into the shaft opening in the vessel wall.
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