Filtration Handbook Filtration and Flushing Strategy

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The exacting tolerances in today’s hydraulic systems require tight control of the system contamination. Experience has shown that impurities found in the system originate from the installation and from new oil. If not removed, particles will cause damage to valves, pumps and bearings and, eventually, lead to malfunction of the system and increased wear on the hydraulic components.

MAN Diesel & Turbo specifies the international ISO 4406 standard to be used when defining the quantity of solid particles in the fluid used in a given hydraulic power system.

ISO 4406

The scale numbers are allocated according to the number of particles per 100 ml of the fluid sample. A step ratio of generally two, as given between the upper and lower limits for the number of particles per 100 ml, has been adopted to keep the number of scale numbers within a reasonable limit and to ensure that each step is meaningful,see Table I.