What types of lubrication can be used for pump bearings?
March 2019 Pumps & Systems Magazine
There are many bearing types, which require different lubrication methods. This response focuses on the most common methods for lubricating rolling element bearings in horizontal process pumps and their application considerations include:
• Grease lubrication:
An advantage of grease lubrication is simplified maintenance, and some disadvantages are over-pressurization and limited heat dissipation. The use of grease is primarily limited to lower speed and horsepower pumps.
• Oil splash:
Some advantages of oil bath/splash lubrication are a wider range of speeds than grease and visual verification of oil level is possible, and some disadvantages are sensitivity to oil level and contaminants remaining in the oil bath. Oil splash lubrication can be achieved by the bearing being in direct contact with the oil, oil rings contacting the lubricant and splashing it throughout the bearing housing, or slinger disks that splash the lubricant throughout the bearing housing.
• Pure oil mist:
Some advantages of pure oil mist lubrication are lower operation temperature compared to oil bath, wear particles are not recirculated and lower oil consumption. Some disadvantages are that it requires higher level of application knowledge and higher initial costs compared to oil bath. The basic concept of oil mist lubrication system is dispersion of an oil aerosol into the bearing housing. There is no reservoir of oil in the housing, and oil rings are not used. The oil is atomized and airflow transports the small oil particles through a piping system into the pump bearing housing.
What methods can be used to maintain lubrication oil quantity and quality?
For oil bath lubrication, quantity of oil can always be adjusted by adding oil to maintain the manufacturer’s recommended level. However, another approach to maintain the proper quantity of oil is with bearing housing seals. When properly applied, bearing seals
can eliminate lubrication leaks from the housing and help maintain recommended oil levels.
Examples are lip seals, labyrinth isolators and magnetic face seals shown in Image 1. These mentioned seals are also useful in the reduction of oil contamination to maintain the quality of the oil.
Particle contamination can be avoided with consideration of materials, design and maintenance of lubricant containers, seals and bearing isolators. When selecting gaskets and seals, materials should be compatible with the lubricant.
When filling the bearing housing, the fill port should be cleaned prior to opening, the lubricant container should be closed until filling, and care should be taken to prevent atmospheric contaminants from entering the fill port during the fill process.
In addition to preventing lubricant leakage, bearing housing seals also serve to prevent contaminant ingress.
Focusing on isolator technology, labyrinth and magnetic face-type bearing isolators are widely used on pumps. Bearing isolators allow increased pressure created in the bearing housing by normal pump operation to vent through the isolator and have proven to be effective at reducing, and sometimes eliminating, contaminant ingress. The face design and the labyrinth design allow for the venting to occur while in operation.
The face design of the magnetic isolator protects the bearings against contaminants while the pump is shut off or in standby using the contacting faces.
Labyrinth isolators may use shut-off features to provide ingress protection when the equipment stops rotating, as shown in Image 2.
These shut-off devices are designed to prevent moisture from penetrating the bearing chamber when the equipment shuts down and air is drawn into the housing.
When properly specified, bearing housing lubrication qualityenhancing components-including oilers, bearing protection devices and vents-can be effective in maintaining the quality of bearing lubricants.
For more information about proper bearing lubrication and maintaining the quality of the lubrication, download HI’s new free white paper “Proper Lubrication Methods for Bearings” at pumps.org/lubrication
HI Pump FAQs” is produced by the Hydraulic Institute as a service to pump users, contractors, distributors, reps and OEMs. For more information, visit pumps.org
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