Oil quality is a decisive factor for the service life of a gearbox. In addition to the type of lubricants used, (e.g. synthetic oil with improved lubricating properties to extend service life) a recent upgrade increases potential to optimize oil quality and extend service life.
Gearbox wear is determined by operating conditions and stresses exerted on components. Hence, gear-oil life is difficult to estimate. Impurities, the degradation of additives, and oil-aging products generated during operation all contribute to premature aging of gear oil.
Most gearbox manufacturers recommend no more than 36 months between oil changes. In some cases, the service life of gear oil is not met due to impurities that cause the main-flow filter to prematurely fail. Research shows that only a small percent of the main-flow filter’s dirt-holding capacity absorbs impurities. This was sometimes due to a deposit of oil-aging products that formed a seal over the main flow filter, causing its failure.
Availon engineers, however, found that a recent kidney-loop filtration upgrade improves oil quality and prevents the need to perform some filter and oil changes recommended by the manufacturer. This reduces downtimes and some costly repairs.
The upgrade was developed for systems with a fine filtration level of 10µ or greater.
As the development’s name implies, kidney-loop filtration provides an oil flow to clean the gear oil independent of the main flow filter. Oil-aging products and particles larger than 3µ are removed from the lubricant. The filter also removes moisture from the oil. Contrary to common thinking, finer filtration does not remove additives. They remain in the gear oil. The upgrade consists of a compact pump and filter unit, installed near the gear coupling or on the gearbox. The unit siphons oil from the lowest point of the gearbox through a hose, cleans oil inside the unit, and returns it to the gearbox.
Availon engineers say installing a kidney-loop filter only takes about four hours. The amount of time between filter exchanges depends on the degree of gearbox-oil contamination. However, the oil’s required purity class, according to DIN ISO 4406, differs between gearbox manufacturers. Evaluation of oil analyses based on samples taken at regular maintenance intervals shows that, during regular operation, a standard gearbox has an oil-purity class of 22/20/17, which is usually a higher degree of soiling than specified by the manufacturer. The oil filter should be replaced six months after installation and then at 12-month intervals. The filter can be replaced during normal maintenance work, depending on its wear.
The kidney-loop filtration unit can extend intervals between gear-oil exchanges to 60 months or more, saving the cost of frequent oil changes. Also, filter changes between regular maintenance intervals are no longer required after installing the upgrade, says Availon. Minimizing costs, maximizing efficiency, and extending the life of such components is crucial in low-wind years. A few turbine manufacturers already include kidney-loop filtration in new models and say the oil change interval depends on the result of an oil analysis.
Filed Under: Lubricants, News, O&M