Meaning
Solid contamination in hydraulic fluid is classified by a standard numbering system that represents particle concentration per unit volume. The ISO 4406 cleanliness code utilizes a multi-tier rating to indicate the quantity of particles of different sizes, focusing on those larger than four and six micrometres respectively. This rating scheme applies to industrial fluid power systems and terminates its utility when fluids contain emulsions or high water content.
It provides a standard language for fluid condition monitoring.
Code Structure
Each number in the triple-scale represents a range of particle counts found in a one-millilitre fluid sample. Incrementing a value on the scale indicates a doubling of the contamination level. This logarithmic scale allows technicians to track small shifts in contamination before component damage occurs.
Production Validation
Scaling up hydraulic equipment assembly lines from prototype testing to full-rate manufacturing requires strict monitoring of fluid supplies. Achieving a low ISO 4406 cleanliness code is a prerequisite for factory acceptance of new machinery. If the system is started with dirty fluid, internal pump wear accelerates, causing early system failure.
Maintenance Consequence
Standard monitoring programs use this rating to trigger filter replacement cycles. Waiting for fluid discoloration before replacing filters is a high-risk strategy that raises overall repair bills. Proper baseline monitoring extends the service life of high-pressure pumps.
