Contamination in hydraulic systems refers to the presence of any foreign substances that are not part of the hydraulic fluid's original composition. These contaminants can be categorized into four types: gas, liquid, viscous, and solid.
When does it become a problem?
Contamination becomes a problem when it exceeds the cleanliness standards required for the hydraulic system to operate efficiently or exceeds any given limits.
Even small amounts of contaminants can cause significant wear and damage to system components such as pumps, valves, and seals. This wear can reduce the efficiency of the hydraulic system, increase downtime, and result in costly repairs.
What are the main types of contamination?
Solid contamination
Solid particles, ranging from metal shards to dirt and debris, are among the most detrimental. They can abrade system components, block passages, and accelerate wear. Read more on solid contamination.
Detection methods include:
- Particle Counting: Quantifies the size and number of particles. (Also counts water, undissolved additives and air)
- Microscopic Examination: Identifies the nature and source of particulates.
Liquid contamination
This type involves the introduction of foreign liquids such as water or other hydraulic fluids. Water can cause corrosion, reduce lubricity, and promote bacterial growth, while other fluids may alter the chemical balance of the system.
Detection Methods
- Visual Inspection: Looks for changes in fluid clarity or colour.
- ICP-OES: Inductively coupled plasma optical emission spectrometry is an analytical method for determining the concentration of elements in a sample. This analysis can detect wear metals, inorganic contamination, and the most common additives. Changes compared to fresh oil provide information about oil health, contamination, and possible mixtures.
- MVA: Microscopic contamination analysis. The oil is usually filtered through a membrane. The dirt remaining on the membrane is then examined under a microscope. This allows an initial assessment of the contamination to be made. If there is a lot of metallic contamination, possibly non-ferrous metal, more hard or soft particles will be visible. Is the residue sticky or varnish-like? This is a quick and easy method of determining the health of the system. Non-ferrous metal, for example, can indicate pump wear. Sticky deposits often indicate mixing or additive degradation. Paint-like deposits are often attributable to oil degradation products.
- Water analysis according to Karl Fischer: Determines the water content in the oil and provides information on whether water-related problems may occur.
Gaseous contamination
Gas contamination typically involves the presence of air or other gases within the hydraulic fluid. This can lead to cavitation, increased fluid compressibility, and efficiency losses. Common sources include improper fluid handling, system leaks, or pump-induced aeration.
Detection Methods:
- Visual Inspection: Looks for changes in fluid clarity or colour.
- Foaming behaviour
- Air separation behaviour
Viscous Contamination
Viscous contaminants often stem from degraded fluid components or cross-contamination with other lubricants. They can alter the hydraulic fluid’s viscosity, leading to poor system performance and increased wear.
In over 90% of all cases, changes in viscosity are due to mixing, contamination or the specification of an incorrect fluid viscosity. Oil ageing also leads to changes in viscosity, but this is the very last parameter to change. Before this, oil ageing is very clearly evident in TAN, ICP-OES and also in the particle count.
Detection Methods:
- Viscosity Testing: Compares the fluid's viscosity against standard levels and fresh oil.
- Chemical Analysis: Identifies chemical changes indicative of contamination.
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