Machinery Lubrication

Machinery Lubrication July - August 2018

Machinery Lubrication magazine published by Noria Corporation

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www . | July - August 2018 | 45 ML higher at the operating tempera- tures, providing a safeguard in case something were to happen in terms of higher operating temperatures or contaminants lowering the oil's viscosity. Reducing the operating temperatures with coolers or other means, or raising the ISO grade can also help you achieve a measure of safety. If the viscosity index were to drop below 108 in this example, you would expect to see advancing signs of wear inside the machine. erefore, you need to know the minimum operating viscosity to set an alarm and limit on that value. Most oil labs test industrial fluids at 40 and 100 degrees C. By using these two parameters, you can calculate the viscosity index and extrapolate the viscosity at whatever in-service temperature the compressor is operating. You should take the approach of setting both upper and lower limits on viscosity, cautionary limits at plus or minus 5 percent, and critical limits at plus or minus 10 percent. Viscosity index could be included as well, as there are many reasons viscosity index could change throughout the life of the oil. Perhaps the most common way viscosity index changes is by shearing down of the viscosity index improver additive. Over time this additive is cut into smaller pieces and loses its impact in the oil. You then see a drop off in the high- temperature viscosity. is generally is measured or monitored by reading the viscosity at two temperatures. While there isn't a set level for viscosity index across the board, you can determine the required viscosity index for your machine and then set limits based on how much the viscosity will drop at a given oper- ating temperature. Remember, with viscosity, in most cases it is better to err on the side of caution and have too much rather than not enough. ML If you have a question for one of Noria's experts, email it to Let Noria help you solve tough lubrication problems and discover the root cause of equipment and lubrication failures. For more information visit

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