"Our plant utilizes a centralized lubrication system, and we are looking to change oil viscosity grades. Do you have any advice on what parameters need to be monitored on this type of lubrication system when changing from one oil viscosity grade to another?"

Obviously, the first parameter to monitor would be the viscosity, which is the single most important physical property of a lubricant. Viscosity determines film thickness and film strength in machines. Some flow sensors like the monitoring and confirmation feedback sensors are viscosity sensitive. 

It may be challenging to remove all of the previous lubricant, which can cause issues due to cross-contamination. Performing a full elemental analysis of both lubricants prior to the changeover would be beneficial. This will establish a baseline for later comparisons.

If the lubricants are from the same manufacturer and family of lubricants but just have a different viscosity, the only parameter that would need to be monitored would be the viscosity. If this is not the case, there are other factors that you should consider, including a change in the viscosity index and oxidation.

Keep in mind that a change in viscosity will have an impact on the lubricating film thickness. Changing to a higher viscosity or too thick of an oil can result in internal oil shearing, which is the process of oils pushing past each other causing increased heat and reduced operating efficiency. Too high of a viscosity can also lead to increased internal fluid friction, higher lubricant pressures, lower flow rates and increased load on electric motors.

On the other hand, oil with too low of a viscosity (thinner oils) can cause boundary conditions. This means the oil film that separates the two working metal surfaces becomes too thin to keep them apart. Even small particles or asperities in the oil will scratch and wear these surfaces, resulting in debris in your machinery. When the viscosity is too low, it can also lead to increased friction between metal surfaces, lower lubricant pressures and higher flow rates.

The best policy when changing your oil viscosity is to test your oils more frequently in order to ensure that you do not end up with a catastrophic equipment failure. You should also contact an industry expert to verify that the oils you choose are appropriate for your machinery based on all the parameters, including ambient temperatures, loads, speeds and flow rates.