Contamination Control and Particle Counting
Around 70 to 80 percent of all hydraulic failures trace back to contaminated oil. Solid particles wear pumps, valves and seals, often unnoticed until breakdown. This guide shows how to keep oil cleanliness under control with particle counting, ISO 4406 cleanliness codes and the right filter rating.
View filters and fluidsHow do you read an ISO 4406 cleanliness code?
Oil cleanliness is stated as a three-number code under ISO 4406, for example 18/16/13. The three numbers count particles per millilitre larger than 4 µm, 6 µm and 14 µm. Each code number represents a size range, and one number higher means roughly twice as many particles. A low code means clean oil.
Which cleanliness class does my system need?
The finer the component clearances and the higher the pressure, the cleaner the oil must be. Servo valves with tight control lands are sensitive to small particles, while rugged gear pumps tolerate more. The table below gives practical guide values as a starting point for filter sizing.
- Always set the target class by the most sensitive component.
- Above 200 bar working pressure, aim one class cleaner.
- New oil is not automatically clean, often 20/18/15 from the drum.
How do you count particles correctly?
For monitoring, an oil sample is analysed either in a lab or with an inline particle counter. Optical counters pass the oil across a laser diode and count the shadow per particle size. A clean, representative sample taken during operation is decisive, otherwise stray particles distort the result.
Frequently asked questions
What does the ISO code 18/16/13 mean?
It is the cleanliness class under ISO 4406. The three numbers give the particle count per millilitre larger than 4, 6 and 14 µm. 18/16/13 is a typical target for standard industrial hydraulics.
Is a new filter enough for clean target values?
Not on its own. The filter must match the target class and be changed regularly. New oil should also be filtered on filling and cleanliness verified by particle counting.
How often should I check oil cleanliness?
For critical systems, monitor monthly or continuously with an inline counter. Rugged systems often need only a quarterly lab sample, plus extra checks after faults or oil changes.
Keep oil cleanliness under control
Our hydraulics specialists help with target class, filter rating and particle counting for your system.
Per ISO 4406
Cleanliness classes and target values clearly explained.
Fewer failures
Clean fluids extend component service life.
Correct rating
Filter choice matched to the most sensitive component.
Expert advice
Hydraulics specialists support your sizing.