![]() ** The diametral clearance is the clearance for the applicable range of shaft diameter. * The shaft diameter is the diameter at the seal fit and “up to” means “up to but not including.” 100 mm) greater than the sleeve bearing clearance. A general rule of thumb suggests that labyrinth seal clearance should be 0.002” – 0.004” (.050 –. Labyrinth seal clearance must always be greater than the bearing clearance. Vertical machines may require less clearance. Galling materials, such as cast iron, may require greater clearance. The table at left is to be used for horizontal machines with bronze/brass labyrinth seals, absent specific clearance recommendations from the manufacturer. Dimensions shown in millimeters are rounded off. Speeds given are synchronous speeds corresponding to the applicable line frequency and winding poles. Suggested clearances for labyrinth seals with oil-lubricated sleeve bearings are provided in Table I: 6), which can be used with rolling or sleeve bearings, and with oil or grease lubrication. ![]() Labyrinth seals: Another commonly used non-contact seal is the labyrinth type (Fig. (Clearance and length values are the same for each example). Non-contact labyrinth seal examples arranged in order of sealing effectiveness. Shaft slingers make contact with the end bracket while the machine is idle and move away from it (by centrifugal force) when the shaft is rotating.įig. These seals combine elements of contact and non-contact seals (see Fig. Example of a shaft-slinger seal that combines contact (1) and non-contact seal types Special long-relief isolators are used in sleeve-bearing applications to accommodate the bearing’s axial end float.įig. This prevents vapor ingress while the machine is off and eliminates friction/heat when it’s running. Labyrinth-design isolators: Another variation of the bearing isolator has a labyrinth design and an O-ring or other elastomer element that keeps the labyrinth channel closed when the shaft is stopped and expands by centrifugal force to open the channel when the shaft is rotating. Although contacting isolators stop all solid and vapor contamination, they have surface-speed limitations-a maximum of about a 4″ (100 mm) shaft at 3600 rpm. 4) uses rare-earth magnets to apply tension to lapped contacting faces, just like a mechanical pump seal. A newer version called a contacting isolator (Fig. Contacting-type bearing isolator ( courtesy of Isomag)Ĭontacting isolators: The first bearing isolators were non-contact labyrinth seals that greatly reduced contamination ingress but didn’t stop moisture or other vapors. Although bearing isolators are more costly and require more physical space than contact or non-contact seals, they deliver more effective sealing.įig. They also can be used with either grease or oil lubrication, and with sleeve or rolling bearings. Such seals afford more protection than individual contact or non-contact seals. 3), but use the contact features to “drive” part of the seal at the shaft’s rotating speed. Example of a combination contact and non-contact bearing isolator sealīearing isolator seals: Bearing isolators combine the characteristics of contact and non-contact seals in a single unit (Fig. Unfortunately, non-contact seals also allow lubricant to leak out of the bearing chamber and liquid, and permit physically small contaminants to enter.įig. 2) produces much less friction (if any) and heating than a contact type. Non-contact seals: A non-contact seal (Fig. Example of a non-contact seal used for a ball bearing If a less effective sealing method is acceptable, an alternative is a non-contact seal.įig. These seals make it difficult for fluids or solids particles to penetrate the sealed area, but direct contact with the shaft creates friction and heat that can degrade the seal and damage the shaft’s surface finish. 1) forms an effective sealed interface by applying continuous pressure to the surface with a resilient material. The contact-grease-seal arrangement on the left is better for protecting against dust and liquids entering bearing chamber the arrangement on the right is better for retaining lubricant in the bearing chamber.Ĭontact seals: A contact seal (Fig. The labyrinth seal is a non-contacting type normally used with sleeve bearings.įig. The types of seals most commonly used with rolling (ball and roller) bearings are contact or lip seals non-contact seals and, to a lesser degree, various types of bearing isolators that combine the functions of contact and non-contact seals in different ways. To select the appropriate seal for an application, match the relevant factors from the above list with the characteristics of the following external seal types. Key factors in making the right choice for an application typically include: The focus here is on what to consider when selecting external bearing seals. Some seals are integral to the bearing others aren’t.
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