Compact long-life magnetic fluid seal

Claim 1

A compact long-life magnetic fluid seal for sealing between a housing and a magnetically permeable shaft, comprising: a magnetic assembly coupled to said housing and comprising an axially polarized annular magnet producing a magnetic field and having a closely-spaced, noncontacting relationship with said shaft to define a first gap, said magnet including an inner surface which defines the outer periphery of said first gap, and an annular pole piece with a first end surface axially abutting a first end surface of said magnet and having a closely-spaced, noncontacting relationship with said shaft to define a second gap, said first and second gaps together defining an annular space between said magnetic assembly and said shaft, said magnetic assembly including means for substantially confining the magnetic flux to said first and second gaps, said confining means comprising the inner surface of said magnet having a generally rounded edge; and a magnetic fluid retained in said annular space by said magnetic field, said magnet and said pole piece being dimensioned so that said first gap has a slightly larger radial dimension than said second gap and so that sufficient magnetic field is provided in said first gap and in said second gap to retain said magnetic fluid in both said first gap and said second gap, said magnetic fluid being retained substantially entirely with said first gap and said second gap by said magnetic field and sealing said shaft and said housing.