What is varnish and why should I care about it?

Varnish is a thin, insoluble film deposit that usually forms on fluid-wetted surfaces inside a turbine lube system, and even on bearings and servo valves.

Varnish is comprised of a wide range of oil additives and high molecular weight thermo-oxidative fluid breakdown compounds that have limited solvency in the base fluid. These compounds are polar in nature and begin to migrate from the base fluid to the wetted surfaces over time, depending on the system and fluid conditions and their polar affinities. The chemical compositions of these insoluble materials may vary depending on the turbine operating conditions or the fluid base stock and additive type.

Initially, these surfaces show up as a gold or tan color and build up to darker gum like layers that eventually develop into a hard, lacquer-like material.

Why Varnish Matters

Varnish is hard to remove and cause ongoing issues for system internals. Some noticeable side-effects of varnish include:

  • Oil that is hard to reclaim or bring down to desired ISO count levels
  • Sticky valves
  • Repeated failure of sensitive internals
  • High contamination levels even after an oil change

In order to address these issues, varnish must be removed from inside your piping, reservoirs and equipment internals.

How to Remove Varnish

Varnish can be removed using several different technologies. We offer Varnish Absorption Skids for rent, but you will want professional assistance in planning a varnish mitigation effort and running the equipment.

A basic overview of varnish removal is:

  1. Analysis to determine current varnish and contamination levels
  2. System cleaner is circulated in the system for a pre-determined amount of time
  3. The system is emptied and reservoirs and cleaned
  4. Filters are changed and base oil is used to charge the system for continued circulation
  5. The system is drained, filters are changed again, and fresh oil is added
  6. A final check is performed
  7. If needed – a Varnish Absorption Skid for continuous side-stream circulation is setup to continue removing varnish over a set period of time.
  8. If VAS is used, additional testing will happen periodically until desired ISO levels are achieved.

For more information on varnish removal, see this whitepaper or call us: 800-770-4510 

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