Water Content by Coulometric Karl Fischer (ASTM D6304)

Contamination of an oil based lubricant by water can damage the metal-to-metal surfaces that the lubricant is designed to protect. The local frictional effects within the lubrication system be it hydraulic, engine, transmission etc, can cause temperatures in excess of the boiling point of water which would in effect cause steam cleaning of the oil away from the surfaces. The boiling of the water or moisture can also promote oxidation in the oil and be blamed for corrosion and poor lubrication on the metal surfaces. Moisture can be sourced from the atmosphere when the compartment is cooling down, engine blow by gasses and coolant leaks.

Using a light scattering principle, particle size analysis for the various micron sizes are computed. A good Particle Size Analyser utilises a laser scanner and can detect particles from 2-400 microns.  Results are presented utilising SAE AS4059 or  ISO 4406 level codings.

An example of standard particle count ranges and the required limits areas are as per the diagram.

Establishing the level of cleanliness enables assessment of the filter effectiveness for clear lubricants only.  Engine oils, due to the dark opaque nature obtained during use, cannot be analysed in this manner.

Retained Solids Content in Hydraulic Oils.

Retained or Total solids content of hydraulic oil is also determined by filtration to 1 micron. By passing the oil through a filter membrane all particles larger than 1 micron are retained. The filter is then weighed and a weight of the filtered material will give us through a calculation, the Retained solids content. Various applications of hydraulics will dictate acceptable solids content but usually retained solids content in excess of 500 parts per million by weight (0.05 %) is considered unacceptable and will indicate that the oil filtration system is either by-passing or ineffective and requires attention.