For almost 100 years the big 3 centrifugal blower manufacturer's always used "open" ball bearings in their blowers. The reasoning was simple-in addition to better dissipation of heat, you can't add grease to a sealed bearing. And every maintenance tech knows, you have to periodically add grease to bearings in any rotating equipment if you want the bearings to last.  

Motor manufacturer's had long ago added a single shield to the back side of some of their motor bearings, probably to keep the grease in the bearing housing-not all over the motor windings. Then they would advise to regularly remove the drain plug to allow excess grease to seep out. For the past few years some motor manufacturers have opted for the completely sealed bearing(side shields on both sides) on their lower HP motors. I've seen totally sealed bearings on new 50 HP WEG motors! I even had one motor repair shop install sealed bearings during the repair of a 200 HP Reliance motor, per the manufacturer's recommendations!!

Gardner Denver has installed sealed bearings in some of their landfill gas blowers. Side shields could obviously prevent bearing contamination, but would it really extend the life of the bearing? In some landfill gas applications, I would have to say yes. Some landfill blowers suffer bearing failures annually because of all the moisture and other contamination in the piping system.  If every year or 2 some blower bearings need to be replaced, side shields could allow another year or 2 of operation.

In WWTP operations, the blowers run much cleaner with the filtered air, so contamination from the piping system is not much of a factor. Sealed bearings here could result in hotter bearing operation, and without the ability to replenish the grease periodically, I suspect the bearing life would not exceed 5-6 years. Compare that with open bearings in blowers that have historically lasted for 20-30 years!

The only reason to install a bearing with one shield, like the motor manufacturers' do, is if the shaft seal is not keeping the dirt and moisture out of the bearing cavity. And since most bearing housings are designed with the zirk fitting to the back of the bearing, the lubrication procedure would have to be changed drastically. This is possible, but certainly not recommended.

Sealed bearings can eliminate the need for preventative maintenance. If you can't do the PM, how are you going to save money? Invest in PM, it will save you money!

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                                                   --- Bill Snyder