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  • Peg Minichiello

How To Prevent Varnish Formation In An Air Compressor 

Varnish is one of the biggest contributing factors to increased energy consumption and lost reliability in an air compressor. Today we will discuss what varnish is, some of the most common causes and preventative measures one can take against it.

What is Varnish?

Varnish is a broad term used to the describe the by-products of lubricant degradation. The black, sticky substance is known to make compressors run hot and is often found in control valves. 

This substance hardens, attracts and retains harmful particulates that, over a period of time, can cause damage to your air compressor. 

Common causes of varnish formation

This seemingly innocuous substance can cause problems when left unchecked. We believe it is necessary to know the main causes, in the hopes of preventing a varnish formation. Causes can include:

  • Heat

  • Over-utilization of lubricant

  • Reactive intake gases

  • Contamination (Caustic chemical, coolant, grease and chloride)

  • Oil Incompatibilities

  • Static discharge

  • Fluid cavitation

  • Hydrolysis

  • Caking on hot surfaces

Preventing Varnish

Preventing varnish is not as easy as one may believe and, unfortunately, it is not always simply a case of picking a high-quality lubricant to do the job for you. You need to have a greater understanding of your oil and equipment.

By performing regular oil analysis on the in-use lubricant you can track lubricant degradation easily. Once you have performed an analysis it is of the upmost importance to act accordingly and change your lubricant when it’s time to.

The three major factors of lubricant properties to monitor are:

  • Total acid number

  • Metal counts

  • Viscosity

There are also qualified oil analysis laboratories that can perform more thorough tests that will identify and quantify varnish within a lubricant.

Some of these tests to identify varnish in equipment are:

  • Ultra-Centrifuge test

  • Blotter spot test

  • Microscopic Particle Counting

  • Colorimetric Analysis

  • Membrane patch colorimetry

  • Colorimetric analysis

  • Sediment & Oil Colour Observation   

Make Your Varnish Vanish

With so many common causes it is inevitable that at some point you will experience the effects of varnish and will have to deal with them.

CDA is an expert on all things air and would love to assist you in tackling your varnish problems. Call us today so we can talk more about your concerns. 925.667.3400/

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