We speak of chemical contamination when foreign substances present in the base fluid attack the materials of the system either chemically or physically.

Physical attack means that the behaviour of components is adversely affected, but the chemical composition of the materials involved remains unchanged. When the composition is changed as the result of chemical reactions, we speak of chemical attack.

Strictly speaking, water and air are also chemical contaminants, since they react with the system materials. However, since air and water both represent such considerable threats to oil (without taken the chemical aspects into account), they are discussed in seperate sections.

One of the main reasons of degradation of hydraulic fluid is oxidation, a chemical reaction between oxygen and hydrocarbon molecules in the fluid. Hydraulic oxidative degradation is rated by the Acid Number (AN) / Total Acid Number (TAN). It displays the amount of potassium hydroxide (KOH) in milligrams that is needed to neutralize the acids in one gram of oil. The acidity of the oil is generally used as a measure of its aging.

Effects acids

  • Fluid gets darker
  • Increased viscosity
  • Development of varnish and sludge

Soft contamination
Soft contaminants are another insoluble contamination type causing problems for a wide range of hydraulic applications, especially turbine applications. Soft contaminants can lead to the formation of varnish. Contaminated fluid containing metal and moisture particles will oxidise, which results in fluid degradation and a rising TAN, and eventually in the formation of varnish.

Varnish creates a sticky film on the components of the hydraulic system, catching all sorts of particles. This continues to build up, forming an abrasive and destructive surface film that results in sticky deposits adhering to the metal surfaces of the oil loop, e.g. piping, valves, heat exchangers, filters and other sensitive equipment. Varnish is one of the most underestimated contaminants that will lead to a reduced service life of your fluids, filters and system and will cause unscheduled downtime and maintenance.

Effects of varnish

  • Less effective heat exchangers
  • Increased wear of valves, load gears, and bearing surfaces
  • Reduced hydraulic fluid life
  • Premature filter change-outs and oil flow restrictions
  • Increased oil leakage

Soft contaminants will also cause sludge, a soft dark substance which moves around in the hydraulic system until coming to rest at the bottom.

Effects of sludge

  • Monday morning disease
  • Clogged of valves
  • Increased operating temperature
  • Corrosion

Chemical deterioration starts with contamination of the oil. Need help getting and keeping your oil clean?
Use the RMF product finder, call +31 180 62 13 13 or contact us.