Patent ID: 7188840

Claim:
A magnetic assembly for use in a multistage magnetic fluid rotary seal comprising: a shaft having a plurality of trapezoidal-shaped ridges along a circumferential portion of said shaft; an annular permanent magnet adapted to surround said shaft; and a magnetically permeable annular first pole piece having a first magnet side and a first pole piece inner diameter, said first magnet side being in a magnetic flux relationship with said magnet, said first pole piece having a plurality of pole piece trapezoidal-shaped ridges along said first pole piece inner diameter wherein a top flat portion of each of said trapezoidal-shaped ridges of said first pole piece is spatially opposed to a flat top portion of one of said plurality of trapezoidal-shaped ridges of said circumferential portion of said shaft, said top flat portion of said plurality of pole piece trapezoidal-shaped ridges being adapted to extend into a close substantially radially aligned and non-contacting relationship with said top flat portion of said plurality of trapezoidal-shaped ridges of said circumferential portion of said shaft wherein said plurality of trapezoidal-shaped ridges form a plurality of trapezoidal-shaped stages, said relationship defining a radial gap adapted to receive a predefined quantity of ferrofluid disposed in said radial gap at said plurality of trapezoidal-shaped stages.