Etesia HYDRO 124D, Техническое учебное пособие

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Debris from components that have been subjected to temperatures that are too high or to cavitation
phenomena should be classified as coarse pollution. This justifies the use of a safety filter whose filtration
fineness is lower than 15
µ
m.
b) Ultra-fine pollution
This corresponds to particles smaller than 5
µ
m.
This pollution, also known as "micronic mud" includes very small metallic particles, but also fluid gels
(paraffin and other additives that are products of oil refining). It also concerns salts and metallic oxides.
As well as the abrasive paste effect, the micronic particles have harmful effects on systems with very
small functional clearances (For example : servo valves). The consequences are as follows :
- Blocking up of small diameter nozzles.
- Clogging slides with sharp edges and no overlap
- Blocking of electrically controlled slides with low clearances.
- Premature wear on roller bearings.
Finally, ultra fine pollution also causes the oxidation of the hydraulic fluid.