Many people wonder whether oil or grease lubrication is best for main gear and bearing assemblies. Jack L. Dillon Jr., assistant director of utilities for the City of Fort Smith, AR, recently faced this decision in specifying a replacement drive.

"I do not have preference as to whether the ball bearings are being lubricated with grease or oil lubricated," Dillon said.Ê "However, our maintenance personnel have expressed displeasure with oil lubrication because they have to drain the condensation and change the oil."

Principles of Lubrication, which is published by Exxon, defines grease as "petroleum oils thickened with special soaps that give them an unusual ability to stay in place. It is often used in applications for which it is not practical to provide a continuous supply of oil." But for longer bearing and gear life, DBS believes that a continuous supply of oil is needed.

For one thing, bearings and gears require regular re-lubrication because of high exposure to contaminants in the air. However, grease cannot be changed easily, and simply adding more grease will not necessarily purge debris and deteriorated grease from the bearing and/or gear system. The presence of such debris and the displacement of grease between the gear mesh can cause excessive gear wear or failures in drive units, which are normally installed in fairly hostile environments. So if, for example, maintenance personnel performed sandblasting operations near a drive unit with grease lubrication, the unit could end up needing a complete overhaul of the bearings and gears.

Grease doesn't entirely eliminate problems with water, either. Condensation still occurs in the housing -- the water simply gets trapped between the steel surfaces and the grease. Oil, on the other hand, is fluid in nature and since drive units operate very slowly (clarifier speeds), water and oil will separate. The water will then collect in the bottom of the housing where it can easily be removed. To prevent water from accumulating in the housing, DBS can even include a CCU (Condensate Control Unit) with drive units.

The bottom line? Since debris and water can be easily removed using oil bath lubrication for the main gear and bearing, and since oil provides continuous lubrication, DBS believes this system is the better alternative.