If you find a little varnish in a hydraulic reservoir, there's probably a lot more distributed throughout the hydraulic system.
Varnish in hydraulic systems starts off as soft, insoluble contaminants that are so small they pass right through filters and go undetected by particle counters. They collect throughout a hydraulic system and can eventually become varnish that causes valve sticking and other system malfunctions.
These insoluble soft contaminants caused by a combination of water, heat, and oxygen. The heat is caused by static discharge, a process discovered several years ago that damages a filter's center core. Now, with additional study, there is solid visual proof that static discharge occurs throughout the entire hydraulic system, causing the formation of tar and varnish and reduced system performance.
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