Varnish is considered a contaminant and can be described as a thin, insoluble deposit occurring on internal components such as valves, bearings, and gears resulting from the oxidation and polymerization of hydrocarbons. The presence of these deposits can result in sticking, seizing or other malfunctions of close-clearance moving parts. The ability to gauge a lubricant's potential to form these harmful deposits requires a specific testing methodology.

NOTE: Electrostatic discharge can sometimes occur due to friction resulting in thermal and oxidative degradation.

Negative Effects of Varnish In A Lubrication System

• Reduced clearance zones diminish the effectiveness of hydrodynamic lubrication. Lubrication efficiency is impeded resulting in increased wear rates of gears, bearings and other internal components.
• Increased friction points. This friction results in greater energy expenditure and can cause valves to stick or clog.
• Increased operating temperatures. Varnish can become an insulator reducing the ability of the lubricant to cool internal surfaces.
• Constriction and reduction of oil flow. Varnish can result in the clogging of valves and filters.
• Component abrasion and internal wear. Varnish captures contaminants, creating a hard grit surface that accelerates wear. When magnified, varnish has the appearance of sandpaper.
• More down time and higher maintenance costs. The results of the effects of varnish are unpredictable and costly.

Diagnosis

Identifying the precursors or "potential" for varnish formation has proven to be very challenging for service technicians and maintenance experts. Traditional methods of oil analysis have proven ineffective in detecting soft contaminants that will ultimately lead to varnish deposits. Until recently, it has not been practical to incorporate anti-varnish testing into a maintenance regime. Industries that run equipment with a greater likelihood of developing varnish should add varnish potential testing to their overall maintenance program.

The method adopted by Fluid Life takes into account a number historical indicators unique to the unit being sampled.

When testing oil, varnish indicators are not identified with standard test methods such as particle counts, acid numbers, etc. In part, this is due to the size of the varnish precursor particles which are typically less than one micron in size.

Fluid Life has developed a Varnish Potential Test that looks at the particles in an oil sample larger than 0.45 microns. The amount and colour of these particles identifies the "potential" of the oil to form varnish and is reported on a scale of 0 to 100, where 100 indicates that severe varnishing will occur.

These sample patches show the increasing degrees of particle contamination and discolouration as severity increases.

For customers using Fluid Life Data Management Products such as WinRoast and MyLab, the photographs of these sample patches are easily viewable and give service technicians another predictive tool in their maintenance program.

Maintenance Solutions

Once a maintenance technician has the testing information to determine if there is varnish potential within a component a course of action can be taken such as:

• Adjusting or optimizing oil change intervals.
• Modifying their maintenance schedule to reduce the chance of varnish formation based on the run time of the specific component.
• Use a side-stream filtration system for use in components that use the same oil for long periods of time. eg. large hydraulic systems and turbines.