Lubricating oil is slightly hydroscopic. This means that at any point in time a small quantity of water is present in the oil.

It is for this reason that special precautions have to be taken when transformer oils are being introduced into the transformer. Specialized equipment is used for this process. Water can exist in lubricants in three states :

  • Chemically combined with the oil
  • Free state ( easily separated by centrifuging)
  • Dissolved state (50ppm is normal)

Water is a common contaminant in hydraulic and lubricating systems. Moisture can enter these systems at several points :

  • Through reservoir breather caps humid air. System fluid absorbs some of this moisture, while some is condensed on the inside surfaces of the reservoir.
  • Through worn seals. Besides humid air, coolant and cutting fluid sprays can enter hydraulic systems through worn rod seals as the cylinder moves. In lubricating systems, these water-based fluids can enter through rotating shaft seals on pumps, machine tool spindles and gear boxes.
  • Throughout heat exchangers. Worn and damaged heat exchangers can allow cooling water leak through seals and ruptured lines into the oil system, vice versa.
  • In new oil. An oil barrel stored outside in a vertical position is likely to collect rainwater around its bung. With changes in temperature , some of this moisture will be sucked into the barrel. Eventually, this water enters the systems fluid when the reservoir is filled.

Lube Tip: Desiccant breathers are vital component of lubricant reliability

Desiccant breathers use filter media to remove particles greater than three microns, and a silica-gel desiccant to remove moisture from the air entering the oil. Studies have shown that 50-70% of lubricant contamination comes from outside the equipment. Most machines are designed to ‘breathe’ so protecting the source of airflow from moisture is extremely important. This is true for most sizes and types of machines.