ISO 4406 Cleanliness Code Chart

What it is

ISO 4406 reports how many solid particles are in a fluid sample as three scale numbers, such as 18/16/13. Each number stands for a range of particle counts per milliliter of fluid. The three numbers are for particles at or above 4, 6 and 14 µm(c). The (c) means the sizes are from a counter calibrated to ISO 11171. A lower number means cleaner fluid.

How to read it

1. The first number is particles of 4 µm(c) and larger per mL.
2. The second number is particles of 6 µm(c) and larger per mL.
3. The third number is particles of 14 µm(c) and larger per mL.
4. Look up each number in the chart to see the count range.
5. Compare the result to the target code from the pump, valve or system maker.

Microscope counts may report only two numbers (6 and 14 µm), written as -/16/13.

Scale number chart (particles per mL)

Key points

• Each step up roughly doubles the particle count. Going from 18 to 21 means about eight times as many particles.
• New oil from a drum is often dirtier than a system target. Filter new oil when filling.
• Servo and proportional valves usually need cleaner fluid than gear pumps. Use each component maker's target.
• Take samples the same way each time, from a live, turbulent line, with a clean bottle.

Common mistakes

• Reading 18/16/13 as a single number or a percentage.
• Comparing counts from an uncalibrated counter with a target based on ISO 11171.
• Sampling from the bottom of the tank or a dead leg.

Governing standards: ISO 4406 (solid contamination code); ISO 11171 (automatic particle counter calibration); ISO 4407 (microscope counting); component manufacturer cleanliness targets.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.