Maintenance Efficiency / 5 min
How Oil Contamination Affects Machine Life
Industrial lubricants start out clean, but contaminate quickly during storage and operation inside machinery. Statistics show that more than 70% of machine wear and failures stem from oil contamination. Even invisible particles can wear systems out from the inside.
Published by: Rotek Technical Content Team
Content is published based on manufacturer technical documentation and equipment requirements as the basis for final selection. This is general guidance and does not replace equipment-specific manufacturer approval.
Review our editorial guidelinesTable of Contents
- - Particle (Solid) Contamination and Wear
- - Water Contamination and Emulsion
- - Air Contamination and Cavitation
- - Filtration and Cleanliness Targets (ISO 4406)
Particle (Solid) Contamination and Wear
Micron-sized silica (dust), wear metals, and particles shed from seals circulating in the system create a sandpaper effect. The tolerances of hydraulic servo valves, in particular, are much smaller (3-5 microns) than a human hair (roughly 40-70 microns). Dust of this size causes valves to jam.
Water Contamination and Emulsion
Water mixing into oil (from moisture or direct contact) weakens the lubricating film. It also accelerates oxidation, causes corrosion, and breaks down beneficial chemical additives in the oil (particularly anti-wear and anti-rust additives) through hydrolysis.
Air Contamination and Cavitation
Undissolved air bubbles remaining in the oil cause cavitation in the pump (bubbles collapsing under pressure). Cavitation creates a loud crackling noise in the pump and causes microscopic particles to break away from metal surfaces.
Filtration and Cleanliness Targets (ISO 4406)
Oil cleanliness is expressed under ISO 4406 with 3 numbers (e.g. 18/16/13). These numbers indicate the particle count in 1 milliliter of oil larger than 4 microns, 6 microns and 14 microns. By-pass filtration systems should be used to meet the ISO cleanliness standards specified in the machine's manual.
Frequently Asked Questions
Is fresh oil straight from a drum completely clean for a machine?
No. Fresh oil from a drum is generally not clean enough for the sensitive valves (servo valves) of hydraulic systems. Oil should always be passed through a mobile filtration unit (filter cart) before being transferred into the machine.
How do we remove water from oil?
Free water can be drained from the tank's drain plug. However, water that has mixed into the oil and turned it milky (emulsified) can only be separated using specialized heated, vacuum-based water separator/dehydration units.
What micron rating should the filter be?
This depends on the machine's sensitivity. While 25-50 micron filters are sufficient for standard industrial reducers, sensitive hydraulic systems such as CNC machines and injection molding machines require fine filters (high Beta ratio) in the 3 to 10 micron range.
Is it better to filter contaminated oil for continued use, or replace it?
If the oil's viscosity, acidity (TAN) and additive package remain within limits (confirmed by analysis), simply filtering and cleaning the oil to continue using it is far more economical and environmentally friendly.