Patent ID: 8328199

Claim:
A device for sealing a shaft for transmitting a predetermined mechanical motion to an interior of a treatment chamber maintained in a predetermined environment from an exterior of the treatment chamber while maintaining the environment in the treatment chamber, the seal device characterized in comprising: a housing through which said shaft penetrates; magnetic force generator for generating a magnetic force in a vicinity of said shaft, the magnetic force generator being disposed between said housing and said shaft; a first magnetism transmission member for transmitting the magnetic force generated by the magnetic force generator, the first magnetism transmission member being disposed adjacent to one side of the magnetic force generator and having a pair of inner flanges projecting from said housing towards said shaft, the inner flanges forming a sealing groove surrounding said shaft; a second magnetism transmission member for transmitting the magnetic force generated by the magnetic force generator, the second magnetism transmission member having an inner flange protruding from said housing towards said shaft, and being disposed adjacent to another side of the magnetic force generator; a slide bush, disposed between the inner flange of said second magnetism transmission member and the shaft, the slide bush being secured to said inner flange so that a very small gap is present relative to an outside surface of said shaft; a seal member for sliding relative to an outer peripheral surface of said shaft, the seal member being accommodated in said sealing groove in a state of at least partially protruding towards said shaft; and a magnetic fluid, held between said shaft and said magnetism transmission member by the magnetic force generated by said magnetic force generator; wherein said sealing groove has a substantially rectangular cross-section passing through a center axis of said shaft; said seal member has four protruding parts projecting towards respective vertices of said substantially rectangular shape of said sealing groove; and two of said protruding parts that project towards said shaft have formed therebetween a fluid-holding groove for holding said magnetic fluid.