FINA Lubricants - Particle Count

Particle Count (PC)

Glossary description: Any of several techniques to categorize particles in a fluid with respect to number and size range.

How the test is performed? A volume of sample is flowed through a small orifice that has a light source on one side, and an optical sensor on the other. Particles interrupt light impinging on the sensor, causing a pulse or “count” to be generated. The duration of the pulse will vary with and relate to size, enabling a categorization or sizing to be determined. A technician (or computer) reads as many as six channels, each set to record a specific size range. The set of results is the Particle Count (PC).

Reporting units: Micron range and count in particles/ml is standard. Two common ranges: ISO (International Standards Organization): 2-5-10-15-25-50 microns; OSU (Oklahoma State Univ.): >10>20>30>40 microns. Current ISO ratings (in the form of xx/yy/zz) are derived from counts obtained at 2 microns, 5 microns and 15 microns.

- Water, silicone antifoam and high opacity preclude an accurate laser particle count, as the sensor is ‘fooled’ into counting silicone and water droplets as particles. If the sample is opaque it is necessary to dilute the sample that may reduce the value of the information. The usual practice when this situation arises is to perform ferrography that is not sensitive to water or opacity. Alternative a patch method can be used. The micropatch method is more expensive whereby a sample of fluid is filtered and a person counts particles on the patch surface under a microscope. Silicone, water and dark color are not a problem by this method.

Sampling technique is more critical for this test than any other, as it is relatively easy to begin with contaminated containers or to contaminate the container as one samples the used fluid. Severe increases in PC without support from other tests might, therefore, suggest verification re-sampling.

Interpretation: Particles come from two sources: Wear and Contamination. It is not always easy to determine which of the two sources applies (seals produce both ‘wear and contamination’ particles), since PC doesn’t identify the nature (shape or composition) of the particles. Nevertheless any particle can cause wear, leading to yet more particles, so that it is essential to control them. For this reason limits are emphasized equally with trends in the evaluation process. The most basic control of particle formation is to service filter systems; this might consist of a filter change, or may involve the use of off-line filtration when levels are deemed too high to control with a simple filter change.

- If abnormal PC levels persist despite standard control methods, additional testing (such as Ferrography or Micropatch) should be undertaken, as excessive wear, rather than contamination may be occurring.

Suggested Application: PC is best applied to systems with filtration control. Hydraulics systems are very amenable. Other systems: compressors, 2 cycle gas engines, auto-powershift transmissions, and other filtered rotary systems.

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