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| | Single-pole-piece ferrofluid seal apparatus and exclusion seal system - Patent 4407508 |
 | | The magnetic-flux path of the single pole piece then proceeds through the one end of the permanent magnet, the single pole piece, the ferrofluid and a magnetically permeable shaft and through the air to the other end of the magnet. |
 | | The seal apparatus is cost-effective in that the assembly of the seal is simply designed, easily manufactured, and the space requirements are such that the seal may be employed readily where space is at a premium, and particularly where the shaft 16 comprises a small-diameter, high-speed shaft, such as a computer-disc-drive shaft. |
 | | 3 shows a single pole piece 26 secured to an annular permanent magnet (not shown), one end of the pole piece having a plurality of ridges 30 thereon, to define, with the permeable rotatable shaft 32, a plurality of ferrofluid seals 28, or to define a multiple-stage seal. |
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