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ISO Cleanliness Guidelines for Hydraulic & Lube Oils

Studies show that approximately half of lost machine life is due to mechanical wear and approximately 80% of mechanical wear is caused by particle contamination in the oil. When oil is kept clean, wear rates go down and component service life goes up.

What is Cleanliness?

When we speak in terms of cleanliness, we often refer to the ISO particle count of the oil. According to the ISO 4406 standard, the ISO particle count is a measure of the number of particles greater than 4, 6, and 14 microns in every milliliter of fluid. The number of particles is then converted to what is referred to as the ISO Code or Range Code. The range code represents the number of particles of a given size in one milliliter of sample. Results from an oil cleanliness testing are typically reported in a three number format such as 18/16/13, where 18 represents the range code representing the number of particles that are 4 microns and larger, 16 the range of particles that are 6 microns and larger, and 13 represents particles 14 microns and larger.

How Can we Measure How Much Particle Contamination is in an oil?

Particle contamination is measured using the ISO 4406 (c) standard. The ISO 4406 (c) standard gives a range code corresponding to the number of particles per milliliter in three difference size ranges:

particles > 4 micron
particles > 6 micron
particles >14 micron

A Cleanliness Code is great, but why do these numbers really matter? Won’t the contaminant be visible in the oil?

The reality is that 4, 6 and 14 micron particles simply cannot be seen with the naked eye. In fact, it’s not until particles get as large as 40-50 microns that we can see them without a microscope. By the time you can see contaminants in your oil, the oil cleanliness has well exceeded what the oil laboratories particle counter can count. This effectively means your oil is not meeting standards and is TOO DIRTY.

How Clean Should Your Oil Be? Set Your Targets.

A teaspoon of dirt in a 55 gallon drum will yield a particle count of 19/17/14; way too dirty for most critical applications. At 19/17/14, a hydraulic system would be considered to be highly contaminated and pump life could potentially be cut in half.
In one year, an ISO 19/17/14 oil in a 50 gpm pump will circulate approximately 1,500 pounds of contaminant through the system!
NEW OIL IS NOT CLEAN OIL. Perhaps one of the most common misconceptions in maintenance and reliability is that the new oil we buy is clean enough for immediate use. New oil from drums or bulk deliveries usually contains anywhere from 2 to 20 times the amount of particles that is acceptable for most lubricated equipment.