Particle Size Distribution

Canonical Definition

The statistical description of the range of particle sizes present in a fluid or airborne contaminant sample, typically expressed as a cumulative count or mass percentage at specified size thresholds. Particle size distribution is measured by laser particle counting (ISO 11171) for fluid contamination and by laser diffraction or sieve analysis for airborne dust characterisation. The distribution determines which particle sizes dominate wear mechanisms and which filter rating is required to control the most damaging fraction.

Engineering Context

In hydraulic systems, particles in the 2–15 µm range cause maximum abrasive damage because they match typical bearing and valve clearances (1–25 µm). Particles below 1 µm contribute minimally to abrasive wear and are not captured by standard laser particle counters. Particles above 50 µm are rapidly removed by sediment and are easily caught by coarse filtration. Filter specification must target the critical 2–15 µm range.

Applicable Standards

Knowledge Center Articles

Related Terms