What is varnish?
Varnish is a soft contaminant consisting of lubricant degradation byproducts smaller than 1 micron in size, not measured by traditional particle counting.
Varnish deposits are thin orange, brown, or black insoluble film deposits that occur inside lubrication systems.
Varnish is a high molecular weight substance that is unstable in oil. Varnish deposits cannot be removed by traditional mechanical filtration.
Why test varnish?
Varnish can cause moving mechanical parts such as servo control valves to stick or get stuck.
Varnish restricts oil flow in small holes.
The varnish can be attributed to heat loss in the heat exchanger due to the insulating effect of the varnish.
Varnish attracts dirt and other larger contaminants, increasing wear and potential component failure.
Varnish is a catalyst for building more varnish. Lubricants deteriorate faster.
How to test varnish?
Membrane patch colorimetry (MPC) is a scale used to measure the color bodies of insoluble contaminants in lubricants.
An ultracentrifuge (UC) spins the oil sample to drive the varnish precursor to the bottom of the test tube. Sediments Use the Visual Sediment Rating Scale.
Remaining useful life (scale) is used to measure active antioxidants remaining in lubricants.
Acid Number (AN) measures the total acid number in a lubricant. Acids deplete antioxidants, resulting in varnish.
Varnish potential monitoring has been developed to include all the tests listed above as well as normal lubricant analysis, including:
Particle count (ISO code) measures particle pollution.
Karl Fischer measures moisture%.
Infrared spectroscopy (FTIR) measures wear metal and additive degradation.
There is no linear correlation between the varnish prediction tests. A UC of 6 is not always correlated with an MPC of 30 and a scale of 45. These may vary due to the life of the product, specific heat exposure, temperature, additive package, and lubricant's base product. Each test measures a different aspect of the lubricant's current state. This is why the lab offers annual all-inclusive testing. Customers want access to as much data as possible to capture potential varnish issues before unplanned downtime occurs. For critical systems for recording varnish potential, varnish potential testing should be performed at least annually and more frequently.
