Bearings are normally lubricated with either oil or grease. Oil mist is another alternative, but recent fugitive emission regulations are making this form of bearing lubrication less desirable. According to the SKF Bearing Company, both oil and grease have a useful life of thirty years at thirty degrees Centigrade (86°F). The Duriron pump company estimates that the L10 life of a radial ball bearing in their end suction centrifugal pump, operating at its BEP(best efficiency point), to be between one and three hundred years.
So what is going wrong with the lubricant and bearings in our pumps? We don’t get a service life any where near those numbers. It turns out that most bearings fail prematurely for only two reasons:
- High heat that caused the lubricant to “varnish” and then form “coke” that will introduce solids into the lubricant.
- Contamination of the lubricant by water, moisture and solids.
The water gets into the bearing from three different sources:
- Leakage from packing. As you know, packing leaks.
- Moisture from a water hose that is being used to wash down the base plate and general area because of packing and other types of leakage. If nothing leaked there would be no need for a water hose to wash down the area.
- Aspiration. A fancy name that means moisture in the air is penetrating into the bearing case when the housing temperature reduces.