Machinery Lubrication

Machinery Lubrication November-December 2017

Machinery Lubrication magazine published by Noria Corporation

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2 | November - December 2017 | www.machinerylubrication.com O il Change s AS I SEE IT Jim Fitch | Noria Corporation Managing the Perils of Short-volume Oil Changes The term "short-volume oil change" (SVOC) relates primarily to circulating oil systems. An SVOC occurs when an oil change (either scheduled or condi- tion-based) only involves draining and refilling the oil in the system tank or sump. All or some significant portion of the oil remaining in the oil lines, hoses, bearings, pumps, filters, actuators, valves, heat exchangers, etc., is not changed. In other words, it is a partial oil change. From a practical standpoint, when oil is drained from machines, there is always some residual amount that, at minimum, occludes to interior surfaces and becomes trapped in low regions, quiescent zones, and other nooks and crannies. For example, after an oil drain, diesel engines typically retain approximately 15 percent of their previous oil. When the engine is refilled with new oil, you end up with an 85-to-15 new-oil-to-used-oil blend. e main concern with this practice is the influence the used oil has on the health of the blended new oil charge. If the used oil was low in volume and relatively healthy, the performance and life expediency of the new oil blend can be acceptable. Conversely, if the used oil was contaminated and/or heavily degraded from extended use, the performance and life expectancy of the new oil blend can be sharply affected. For instance, it takes less than 5 percent oxidized oil mixed with new oil to reduce the oxidation stability of the new oil by more than 90 percent. Why Perform a Short-volume Oil Change? ere are several good reasons to perform an SVOC. One is that it's simply less disruption to the system. is includes avoiding the risk of dry start conditions and associated accelerated wear when the machine is restarted due to delayed lubrication (dry start). ese conditions are the result of the time required to refill the lines and components with oil, purging out air, etc. Of course, many large systems have auxiliary pumps that pre-lube the system. Other machines may not have this feature. Furthermore, performing a complete system drain can disturb sludge, sediment and deposits. To read more about this, see my article on oil flushing tips to address the fishbowl effect at MachineryLubrication.com. Unless these solid impurities can be fully purged from the system, they can mobilize within the machine and cause new problems (e.g., motion impediment, restricted It takes less than 5 percent oxidized oil mixed with new oil to reduce the oxidation stability of the new oil by more than 90 percent." "

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