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|October 16, 2002
In This Issue:
Up Front: Take Care of the Little Things
Book Bits: Bearing Lubricant Selection
Today's Tip: Reservoir Baffles and Settling Zones
Q & A: The Fate of Additives
It is surprising how simple methods of controlling oil contamination are often overlooked. Companies may commit considerable resources to solve fluid contamination problems with additional filtration equipment, while little or no effort is made to determine the source of the contamination.
A case in point is turbine lube systems that have vapor extractors. These systems maintain a continuous, partial vacuum on the lube oil reservoir to extract smoke and oily vapors from the system. When working on dirty systems, it is common to find the gaskets on manways and reservoir covers to be severely cracked, or sometimes missing.
A failed or missing gasket may allow hundreds of cubic feet per day of dirty, moist air to be drawn into the lube system. This condition will negate even the best efforts at controlling oil contamination problems.
Keeping oil clean is a must to maintain a competitive advantage in today's market. Sometimes, by not forgetting the all-too obvious simple things, you can reap great rewards. Check your gaskets! (Submitted by Bob Picek, Lormar Reclamation Service. Thanks Bob!)
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From "Rolling Bearings Handbook and Troubleshooting Guide":
When bearings must operate in a wide range of temperatures, use an oil that has the least viscosity change with changes in temperature -for example, an oil with a high Viscosity Index (VI). In many applications, pure mineral oils are most satisfactory. They should be free from contamination, and they should resist oxidation, gumming and deterioration by evaporation of the light distillates. Finally, they must not cause corrosion of any parts of the bearing during standing or operation.
about "Rolling Bearings Handbook and Troubleshooting Guide".
Reservoir Baffles and Settling Zones. Baffles are used to prevent fluid just returned to the tank from passing directly back to the pump inlet. For a number of reasons, a longer transit path is considered beneficial; it encourages better heat conduction from the fluid, better contamination and air separation, and better mixing with the bulk fluid. This is usually accomplished by separating the inlet and outline by as long of a flow path as feasible.
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"What happens to the additives in oil over time, and is there any way to replenish them?" - Cory C. Cousineau, Engineered Machined Products
Over time, additives are depleted performing the function for which they were intended, degraded by hydrolysis, mechanical shearing, condensation settling, water washing, particle scrubbing, etc.
The rate of depletion or degradation depends upon the application and the environment. In particular, heat, pressure, shear rate, fuel sulfur, soot, dirt, water, aeration and the presence of catalytic metals (copper, iron, etc.) affect the rate of depletion.
Regarding replenishment - whenever you top-up a system, you are replenishing additives. Likewise, one can perform a partial drain and replacement (often referred to as bleed and feed).
A bleed and feed can work if the base oil is not degraded. If the base oil has been degraded, adding new oil is analogous to sending a healthy person into a room full of sick people with the hope that his or her good health will be contagious - it doesn't work that way. The additives in the new oil might be compromised within the first hours of use, leaving you right back where you started.
Casual addition of additives into a formulated oil can be dangerous and should be avoided. When in doubt consult your lubricant supplier.
Drew Troyer, Noria Corporation
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