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Bearing Design Considerations for Pumps and Compressors – Part 4

Bearing Design Considerations for Pumps and Compressors – Part 4

We have come to the final installment of our feature article on design considerations for bearings used in pumps and compressors. We hope the previous posts have provided you with a clear understanding of bearing loads and life, bearing fits, and material options to evaluate when specifying a bearing for your turbomachinery application. In this final entry, we examine the importance of selecting proper bearing lubrication.

The following is Part 4 of a four-part post. Links to previous parts: Part 3, Part 2, Part 1.


Appropriate bearing lubrication is one of the most critical factors in ensuring bearings achieve their required design life. Designers of pumps and compressors must consider the most suitable lubricant for the operating environment, as well as the method of lubrication, when specifying a bearing. The life adjustment factor a3 = 1 assumes that the loads, speed of rotation, and lubricant characteristics all contribute to maintaining a constant thin fluid film between the balls and raceways.  

Grease lubrication is commonly used for ball bearings. Bearings are often lubricated “for life” by the manufacturer due to the design configuration and/or constraints. Some designs may include grease fittings, which allow for bearing lubrication at regular maintenance intervals. Temperature range, load, and speed are the primary considerations when selecting a lubricant. Bearing manufacturers typically lubricate ball bearings with a standard all-purpose grease that is suitable for most applications. However, it is a best practice to always consult with an engineer to either ensure the standard lubricant is appropriate or to select an alternate lubricant for optimal life and performance. Grease lubricants consist of a base oil and thickener, and often contain additives. Many different types of base oils, thickeners, and additive packages are commercially available to address a variety of operating conditions including:

  • High and low temperatures
  • High speeds
  • High loads
  • Moisture and humidity
  • Vacuum 

Designers should select sealed or shielded bearings whenever possible. These enclosures prevent contaminants from entering the bearing and assist with grease retention. Single lip seals are most common, but double and triple lip seals are very effective at preventing moisture and liquids from entering a bearing. There is a trade-off, however: using these multiple lip seals lead to an increase in torque, friction, and heat generation during bearing rotation.

Oil lubrication is effective in high speed and high temperature applications, providing excellent cooling properties. Unlike grease, oil should never be considered a lubricant “for life” option for bearings. Oil lubrication requires a continuous flow of oil supplied to the bearing. The oil bath lubrication method is commonly used in larger, slow speed compressors and pumps. By design, the bearings are either partially or completely submerged in an oil bath. Oil mist lubrication, used in high-speed applications, involves injecting a fine mist of oil into the bearing. Oil mist lubrication offers better heat dissipation than an oil bath. As with grease lubricants, selecting the proper oil is crucial to optimal bearing performance. Oil lubrication systems should include filtering and continuous monitoring of both the quality and amount of oil.  


Proper bearing selection is one of the main factors in achieving reliability and longevity from turbomachinery. Application loads, bearing load ratings, and the selection of proper bearing fits, material, and lubrication all must be evaluated to achieve the required life of the equipment. Periodic maintenance and re-lubrication are also important for trouble-free operation. Pump and compressor failures are costly and difficult to repair. A thorough analysis of the application will provide guidance on both proper bearing selection and preventative maintenance, leading to the optimal performance of the machinery.