Solid contamination is often considered as the biggest cause of hydraulic and lubrication failure. Water in hydraulic oil can have just as destructive an effect on the system as solid contaminant particles. Nevertheless, contamination by water is seldom recognized as such. Damage due to water is usually ascribed to some other cause. Water is often associated with other types of contamination. It attacks both the hydraulic oil and the components of the hydraulic system and these two forms of attack reinforce one another.

The water concentration in a hydraulic fluid is marked as RH percentage (relative humidity), ppm (parts per million) or % (percentage).

The occurrence of water in oil
Unfortunately, water is always present in hydraulic oil, since it is naturally soluble in practically all fluids. Small amounts of water can dissolve entirely in the oil. The dissolved water is invisible and does less damage than concentrations above the saturation point.

Above the saturation point, water can be present in the free state and emusified with the oil. It can be detected by the turbidity it produces in the fluid. Small amounts of water produce a slight cloudiness in the fluid compared with the water-free fluid or fluid with dissolved water. Larger amounts give the fluid a milky appearance. This visible water is an emulsion and is highly destructive.

Water in free state generally separates out from the base fluid under the influence of gravity. When the specific gravities are roughly equal (as in silicone-based fluids), the free water floats as droplets in the fluid. When the base fluid is heavier than water (e.g. phosphate esters), the free water floats on top of it.

Saturation point
Each type of oil has its own ‘’saturation point’’ at which oil can’t hold any more water molecules. The saturation point in hydraulic oil lies between 200 and 300 ppm and that in lubricating oil between 500 and 600 ppm.

Maximum saturation level
To minimise the damaging effects of emulsions and free water, the concentration of water in oil should be as low as possible and well below the oil saturation point. We recommend a maximum saturation level of 40-50% at operating temperature for H, HL, HLP and HVLP fluids. Dielectric fluids should be maintained at an even lower saturation level.

Effects of water contamination
The first sign of water contamination is a change in viscosity. This will result in reduced lubrication thickness causing metal-to-metal contact. The combination of free water with small copper or iron particles created by wear will have a catalytic effect on the oxidation.

Free water also penetrates microscopic pores in the metal surfaces, causing corrosion of the system’s components. Corrosion particles will spread through the system, causing the formation of new corrosion in the tank and the cycle continues.

Water contamination will also cause depletion of additives which results in loss of dielectric strength, oxidation, accelerated metal surface fatigue and oil breakdown.

Water contamination can be recognised by:

  • Condensation in tank
  • Rust in tank and oil circuit
  • Pump cavitation & erosion

Water contamination effects:

  • Oil oxidation & deterioration
  • Reduced lubricating film thickness
  • Corrosion
  • Accelerated metal surface fatigue
  • Loss of dielectric strength in insulating oils

We have lots of experience and excellent products to solve waterproblems:

Prevent moisture from entering the reservoir with RMF desiccant breathers. Use RMF fiberglass + polymer filter elements or RMF filter element H2O sorb for absorbing water from the oil. And for oils with waterlevels way beyond its saturation point you can use the RMF vacuum dehydration units.

Have a look at this project: Filtration of water from biodegradable hydraulic oil. Or download the case study.

Tip: check out the RMF product finder to find the best suitable products for your application!

More information? Please call +31 180 62 13 13 or contact us.