The amount of contaminant contained in a fluid is identified by the level of contamination of a system. This parameter denotes a fluid unit volume. The level of contamination may vary depending on where you are in the system. According to the information in the preceding paragraphs, the level of contamination is also heavily influenced by the system’s working conditions, working years, and environmental conditions.

What is the size of the contaminating particles must we deal with in our hydraulic circuit?
Contamination level analysis is significant only when performed in a consistent and repeatable manner, using standard test methods and appropriately calibrated equipment. To that end, ISO has issued a set of standards that allow tests to be performed and the measured values to be expressed in the following ways.

● ISO 4405 GRAVIMETRIC LEVEL
The contamination level is determined by weighing the particles collected by a laboratory membrane. The membrane must be cleaned, dried, and desiccated according to the Standard’s fluid and conditions.
A suitable suction system is used to filter the volume of fluid through the membrane. The contaminant’s weight is determined by comparing the weight of the membrane before and after fluid filtration.

● ISO 4406 CUMULATIVE DISTRIBUTION OF PARTICLES SIZE
The contamination level is determined by counting the number of particles of specific dimensions per unit volume of fluid. Automatic Particle Counters are used for measurement (APC).
Following the count, the contamination classes, which correspond to the number of particles detected in the unit of fluid, are determined. ISO 4406 and SAE AS 4059 (Aerospace Sector) regulations govern the most common classification methods. Although obsolete, NAS 1638 is still in use.

CONTAMINATION CLASSES BY NAS 1638 (January 1964)
The NAS system was created in 1964 to define contamination classes for contamination found in aircraft components. This standard’s application was extended to industrial hydraulic systems simply because nothing else existed at the time. Rather than using cumulative counts as in ISO 4406, the coding system defines the maximum number of 100 ml volume allowed at various size intervals (differential
counts). Although the standard does not guide on how to quote the levels, most industrial users quote a single code that is the highest recorded in all sizes, and this convention is used on MP Filtri APCs.The contamination classes are denoted by a number (ranging from 00 to 12) that represents the maximum number of particles per 100 ml counted differentially in a given size bracket.

ISO 4407 CUMULATIVE DISTRIBUTION OF PARTICLES SIZE
The contamination level is determined by counting the number of particles collected by a laboratory membrane per unit of fluid volume. A microscope is used to make the measurement. The membrane must be cleaned, dried, and desiccated by the Standard’s fluid and temperature requirements. Using a suitable suction system, the fluid volume is filtered through the membrane. The contamination level is determined by dividing the membrane into a predetermined number of areas and counting the contaminant particles with a suitable laboratory microscope.

Contact Us