Got varnish? We have answers

Many of today's hydraulic systems contain insoluble contaminants, which are too small to be trapped by filters — and too small to be detected by particle counting. This varnish formation is a serious problem that degrades system operation.

Alan Hitchcox Blog

April 7, 2014

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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About the Author

Alan Hitchcox Blog

Editor in Chief

Alan joined Hydraulics & Pneumatics in 1987 with experience as a technical magazine editor and in industrial sales. He graduated with a BS in engineering technology from Franklin University and has also worked as a mechanic and service coordinator. He has taken technical courses in fluid power and electronic and digital control at the Milwaukee School of Engineering and the University of Wisconsin and has served on numerous industry committees.