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Herein, a divergent stepped magnetic fluid seal with a single magnetic source is designed to improve the pressure capability of ordinary magnetic fluid seal under small clearance. To explore the effects of injection volume, axial clearance, radial clearance, axial tooth number and radial tooth number on divergent stepped magnetic fluid seal, the pressure capability of magnetic fluid seal with an ordinary structure was comparatively analyzed through experimentation. According to the experimental results, there is no leakage or ejection of magnetic fluid from the sealing device when the critical pressure of divergent stepped magnetic fluid sealing is reached. The divergent stepped magnetic fluid seal structure performs better in pressure resistance the magnetic fluid seal with an ordinary structure. Also, the existence of axial teeth in the stepped magnetic fluid sealing structure leads to an increase in polar teeth, which not only extends the leakage path of the sealing medium but also exacerbates energy loss for the magnetic fluid carried by the sealed medium. This is effective in improving the pressure resistance of the magnetic fluid seal. When the axial tooth number reaches or exceeds the radial tooth number and the axial clearance falls below the radial clearance, the divergent stepped magnetic fluid seal with small clearance has a pressure capability that is 4.1–6 times higher than the critical pressure of ordinary magnetic fluid seal. When the axial clearance exceeds the radial clearance and the axial tooth number falls below the radial tooth number, the divergent stepped magnetic fluid seal has a critical pressure that is 1.9–3.6 times higher than that of conventional magnetic fluid seal.

This paper investigates the failure mechanism of a divergent magnetic fluid seal (MFS) with staggered pole teeth (SPT). By pole teeth, we mean the teeth machined on the inner ring surface of the pole pieces, which have a magnetic field gathering effect. A sealing apparatus capable of directly visualizing the surface deformation of the magnetic fluid film is developed, and the sealing mechanism is studied through experiments. The magnetic field distribution of the sealing apparatus is numerically analyzed to calculate its theoretical value, and this is compared against the experimental observations. The impacts of the eccentricity distance of the axial pole teeth and the addition of magnetic insulation materials on the pressure resistance of the MFS–SPT structure are investigated. The results show that, during the pressure loading process, the magnetic fluid moves to the low-pressure side. When the seal fails, micro-leakage and complete leakage occur successively in the MFS–SPT structure. There is good agreement between the experimental and theoretical pressure resistance of a divergent MFS–SPT. As the eccentricity distance of the axial pole teeth increases, the pressure resistance of the divergent MFS–SPT is enhanced. The sealing performance of the divergent MFS–SPT structure is improved when a magnetic insulation material is added to the grooves of the axial teeth.