On-site fillable liquid magnetic seal

Abstract

An on-site fillable ferrofluidic seal comprises a ferrofluidic seal having at least one ferrofluid conducting channel extending through either the magnet, through one of the pole pieces which sandwich the opposing pole ends of the magnet, or through both the magnet and a pole piece. The conducting channel extends to a location where deposited ferrofluid will be drawn to the gaps between the pole pieces and the shaft. In another embodiment a multi-stage seal is filled by displacing the pole piece/magnet assembly axially relative to the shaft so that each pole piece projection falls halfway axially between two shaft projections. The displacement alters the normal magnetic field pattern to create a substantially uniform magnetic field throughout the pole piece/shaft interface region such that ferrofluid can be drawn through the region. When the shaft is returned to its original position with respect to the pole piece/magnet assembly, that is, when the pole piece projections are re-aligned axially with the shaft projections, a series of stages of the multi-stage hermetic 'O-ring' seal are created. An alternative embodiment of the invention uses the capillary action of the liquid to maintain a multistage seal which holds the liquid in place using axially aligned wettable and non-wettable surfaces on a shaft and stator surrounding the shaft. With the wettable surfaces of the shaft axially aligned with those of the stator, the liquid congregates in the gaps formed between the wettable surfaces of the shaft and stator. Filling of the seal is accomplished by displacing the shaft relative to the stator such that each wettable surface on the shaft axially overlaps two wettable surfaces on the stator, thus providing a path of wettable surfaces which allow the liquid to flow along the length of the seal.