In modern times many hydraulic equipment manufacturers specifies the new oil cleanliness, depending on the hydraulic application. At sensitive components and high working pressure, the required cleanliness is more stringent than a decade ago. For performance servo and high-pressure systems is recommended oil cleanliness according ISO4406 of 16/14/11 or better. One of the causes of ingress of contamination into a hydraulic system is by introducing unclean new oil.

The ISO code 4406 is nominated into three figure numbers, representing the measured number of particles in sizes of 4, 6 and 14 µm. For example, from a 100ml oil sample the following has been measured: 4micron= 25.324, 6micron=6.257 and 14micron=337 particles. 

The ISO4406 code= 15/13/9. [note: 1µm= one micron meter

Source: Noria-USA. 

Another nemesis of hydraulic oil is water. Water creates havoc in a hydraulic system and can be found in three stages: dissolved, emulsion and free-water. The content of dissolved water in the oil depends on the temperature, the higher the temperature the higher the saturation level. Above saturation level water will be present in the state of emulsion and/or free-water. The recommended water content in hydraulic oil by most hydraulic equipment manufacturers is to keep it well below the saturation point.

In a bulk tank storage unwanted ingress of particles and moisture can compromise the cleanliness of the oil. This can be avoided by the installation of an off-line filtration system that removes the fine particles and absorbs the moisture out of the oil. This to ensure that the new oil meets the prescribed specifications of the equipment manufacturer.

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