Water can be present in lubricants as free, dissolved or emulsified water. Because of the different chemical properties, oil and water do not mix but separate in two distinct layers. As water has a higher density than oil, free water accumulates at the bottom of the lube system. However, depending on the composition of the base stock and the type of additives, different lubricants can hold very different amounts of water in dissolved phase (note that temperature and pressure also have effects on how much water a fluid can hold).
Beyond the saturation level of the lubricant, water is present as either free water or emulsion. Emulsion is the state where water is sheared and suspended in the oil as tiny droplets by agitation. The presence of emulsifying additive in the oil can also lead to emulsion formation.
In our white paper, The Impact of Water Contamination on Lubricants, you’ll learn about the effects of contamination (such as rust, vaporous cavitation, and foaming), the oil analysis tests to indicate their presence (e.g. Crackle Test, FTIR), the recommended corrective actions and best practices for minimizing contamination (e.g. lubricant products, desiccant breathers).