Nonbursting magnetic liquid seals for high vacuum applications

Claim 1

A single pole, ferrofluid magnetic seal apparatus adapted to provide a ferrofluid pressure-type seal about a shaft extending between a first low-pressure and a second high-pressure environment, which seal apparatus comprises: (a) an annular permanent magnet having poles of opposite polarity and adapted to surround the shaft to be sealed; (b) first and second magnetically permeable pole pieces, each having a one and another end, the one end of each pole piece in a magnetic-flux relationship with the opposite poles of the permanent magnet, the other end of each pole piece adapted to extend into a close, noncontacting relationship with the surface of the shaft to be sealed, to define a radial gap at the end of each pole piece, the other end of the second pole piece forming, with the surface of the shaft to be sealed, a plurality of separate stages in the radial gap under the second pole piece; (c) a ferrofluid retained in the radial gap under the second pole piece between the separate stages, the ferrofluid adapted to provide a plurality of separate O-ring ferrofluid seals about the surface of the shaft to be sealed in operation, and the radial gap under the other end of the first pole piece essentially free of ferrofluid; and (d) the second pole piece adapted to be placed toward the high-pressure environment and the first pole piece adapted to be placed toward the low-pressure environment, and having a radial gap substantially less than the radial gap under the second pole piece, thereby providing a single pole, ferrofluid, pressure-type seal apparatus having a reduced tendency to permit air bursts, when installed about the shaft and between the first low- and the second high-pressure environments.