Bearing Isolators

Bearing isolators are dynamic seals designed to protect bearings from outside contaminants.  They are comprised of a rotor (rotating) and stator (stationary) member.  Some bearing isolators are of labyrinth construction while others use O-rings or other positive seals.   The most important specifications to consider when searching for bearing isolators are the dimensions.  These include shaft outer diameter or seal inner diameter, housing bore diameter or seal outer diameter, and axial cross section or thickness.  The shaft outer diameter or seal inner diameter refers to the size of the seal inside diameter or the shaft or piston outside diameter.    The housing bore diameter or seal out diameter refers to the size of the housing bore diameter or the seal outside diameter.  The axial cross section or thickness refers to the axial cross section, or thickness, of the seal.

Important service limit parameters to consider for bearing isolators include maximum operating speed, maximum operating pressure, operating temperature, and vacuum rating.  The maximum operating speed is generally given as ft/min or m/sec.  The maximum pressure specifies the maximum pressure that the seal is rated for without failure.  The operating temperature refers to the full-required range of ambient operating temperature.  Some seals or bearing isolators are rated to operate in a vacuum.  Common seal features found on bearing isolators include spring loaded, integral wiper or scraper element, and split seal.  Spring loaded seals are also called spring-energized or having a garter spring. The spring helps keep the sealing lip in contact with the shaft.  Bearing isolators can have a wiper or scraper (exclusion) element in addition to primary seal.  Frequently an oil or hydraulic seal will also have a wiper or scraper element to keep contaminants from the sealing area.  The split in an elastomeric seal facilitates assembly.  A split rigid (metallic) seal is similar in functionality to a piston ring.

Common materials of construction for the sealing element or lip material include none or clearance or labyrinth construction, ethylene acrylic, fluoroelastomer, fluorosilicone, nitrile, highly saturated nitrile, nylon or polyamide, polyacrylate, polychloroprene, polyetheretherkeytone, polyoxymethylene, polyurethane or urethane, natural rubber, sintered bronze, cast iron, stainless steel, felt, or leather.  A polymer is a solid, nonmetallic compound of high molecular weight the structure of which is composed of small repeat units (mers). Plastics and elastomers are polymers.  Many seal manufacturers use their own proprietary material. Where possible, these materials have been categorized into the generic equivalent or material family. Consult with manufacturer for proprietary material specifications.

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