What characteristic of hydraulic fluid is often assessed to determine its cleanliness?

The cleanliness of hydraulic fluid is primarily assessed through its contamination level. The contamination level indicates the amount and type of particulate matter, water, and other impurities present in the hydraulic fluid. Clean hydraulic fluid is essential for the reliable operation of hydraulic systems, as contaminants can lead to wear, reduced efficiency, and potential failure of components.

Contamination levels are typically evaluated using various methods, such as particle size analysis and filtration tests, to ensure that the fluid meets the required cleanliness standards for safe and effective operation. Maintaining an acceptable contamination level is crucial for extending the life of hydraulic systems and ensuring their performance.

While total analysis number (TAN), acidity or alkalinity, and viscosity index are important characteristics of hydraulic fluids, they do not specifically measure cleanliness. TAN relates to the degradation of oil, acidity or alkalinity describes the chemical properties, and viscosity index correlates with the fluid's change in viscosity with temperature but does not directly indicate contamination. Therefore, focusing on contamination level provides the most relevant assessment of hydraulic fluid cleanliness.