Occasionally I receive questions on the use of oil analysis as a PM tool for Centrifugal air & gas blowers. Usually it is from engineering departments, or other office personnel, wanting to know if doing oil analysis will save them money. Although every situation is different, the bottom line is it probably won't truly save money. At least not enough to justify the expense of contracting for periodic oil analysis.
Oil analysis is used in PM to measure the condition of the lubricating oil. It was primarily designed to monitor the oil in engines and gearboxes to better determine whether the oil truly needed changing, or if it could wait for another few months. When you are replacing 20 - 30 gallons of oil at a time, at a cost of $10 - $100 / gallon, you don't want to change the oil unless you are sure it is bad(no longer lubricating your equipment effectively). Oil analysis in these factories is easily justified for this type of equipment.
Centrifugal blowers don't hold much more than a quart of oil at each bearing, except some of the +500 HP units may hold 2 quarts at each end. The oil is relatively inexpensive, so the manufacturer's recommendation of replacing the oil once per year is a safe bet. In high humidity, more frequent oil changes may be required to eliminate moisture buildup in the oil.
During an oil analysis, a spectrometer is used to measure the levels of various metals in the oil. The viscosity of the oil can tell how much 'life' is left in the oil, and the amount of abrasive solids can predict how much longer the components will last. Since I don't actually do any oil analysis, I will leave tribology--the study of wear in machinery, to interpretation by tribologists.
The oil mist lubrication system used in most centrifugal blowers works well to carry away contamination and debris and keep it from the bearing. Visual inspection of the oil drained from the bearing will go a long way to telling you the condition of the bearing.
However, the key is still to regularly monitor the bearing and its' lubrication. Invest in PM, it will save you money!