After completing this subtopic, students should
have learned the following:
- In order to ensure the reliability of any
hydraulic system, standards have been established to determine the
level of cleanliness ( or contamination) of the hydraulic fluids
used in the system.
- The particles of each of the 5 size ranges
should be counted and compared to the maximum number allowed in
the standards, to determine the overall cleanliness class of the
- Depending on the industry, one of the 3
standards should be used (NAS, ISO, or AS).
- It is imperative to be consistent in performing
the entire process, including drawing the sample, preparing it for
counting, as well as the counting and calculating procedures.
- ISO 4406 - "Method for Coding the
Level of Contamination by Solid Particles"
- ISO 4407 - "Determination of Particulate
Contamination by the Counting Method using a Microscope"
- NAS 1638 - "Cleanliness Requirements
of Parts used in Hydraulic Systems"
- AS 4059 Revision F - "Aerospace Fluid
Power: Cleanliness Classification for Hydraulic Fluids"