Present Limits Of Operation Of Product Lubricated And Magnetic Bearings In Pumps
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Interest in nonoil lubricated bearings is growing, due to a number of benefits derived from these bearings: improved pump performance and reliability, enhanced pump maintainability, elimination of the cost and maintenance of separate systems for lubrication oil and shaft seals, reduction in pump size and weight, reduced power consumption, elimination of oil disposal costs, elimination of potential for product contamination, and elimination of leakage of hazardous fluids to the environment. This trend has allowed two types of nonoil lubricated bearings to grow in favor: 1) bearings lubricated by the process media and 2) magnetic bearings. The state-of-the-art in these different technologies is applied to pumps, is examined to identify what the current limits in the application of these technologies are. In the case of product lubricated bearings, the present mechanical limits, film thickness, and temperature limits, as related to different material and lubricant combinations, are reviewed by reference to bearing theory of operation and actual pump application. The role of various lubricant and material properties and mechanical design features are reviewed for these types of bearings. In addition, the importance of proper lubricant circulation and filtering is highlighted. The relationship of the above design parameters to specific load, speed, and temperature is examined to produce limiting operating envelopes for these types of bearings, similar to that previously developed for oil lubricated tilting pad bearings. Magnetic bearing applications completely circumvent the dry running and contamination issues raised by product lubricated bearings and offer unmatched capabilities in pump diagnostic. Space envelope and cost are usually not as favorable as product lubricated bearings. Limitations in operation of magnetic bearings are related to specific load, frequency, temperature, and system stability. The development of limiting envelopes of operation for magnetic bearings is presented to allow pump designers and end users to assess bearing load capacity vs frequency characteristics. Control of rotor and stator natural frequencies often demands special attention to any given application. In certain submerged bearing applications, corrosion considerations represent the most restrictive limitation in the application of magnetic bearings. In theory, almost any type of process fluid may be handled with magnetic bearings, and a growing variety of applications have already been successful.
Swann, Michael K.; Watkins, Jonathan; Bornstein, Kevin R. (1997). Present Limits Of Operation Of Product Lubricated And Magnetic Bearings In Pumps. Texas A&M University. Turbomachinery Laboratories. Available electronically from