ISO 4406:2017
ISO Cleanliness Codes use three separate numbers, for example:
16/14/11
Each number represents the quantity of particles above a particular size within a fluid sample:
- The first number, 16, refers to particles larger than 4 microns.
- The second number, 14, refers to particles larger than 6 microns.
- The third number, 11, refers to particles larger than 14 microns.
Because particles larger than 6 and 14 microns are also larger than 4 microns, they are included within the first particle count.
In the same way, particles larger than 14 microns are also included within the 6-micron reading.
The third number represents the count of particles larger than 14 microns.
How the ISO Code Is Calculated
The table below shows the particle count ranges within a 100 ml fluid sample and how the individual code numbers are obtained.
| Code | Particles From | Particles Up To |
| 24 | 8,000,000 | 16,000,000 |
| 23 | 4,000,000 | 8,000,000 |
| 22 | 2,000,000 | 4,000,000 |
| 21 | 1,000,000 | 2,000,000 |
| 20 | 500,000 | 1,000,000 |
| 19 | 250,000 | 500,000 |
| 18 | 130,000 | 250,000 |
| 17 | 64,000 | 130,000 |
| 16 | 32,000 | 64,000 |
| 15 | 16,000 | 32,000 |
| 14 | 8,000 | 16,000 |
| 13 | 4,000 | 8,000 |
| 12 | 2,000 | 4,000 |
| 11 | 1,000 | 2,000 |
| 10 | 500 | 1,000 |
| 9 | 250 | 500 |
| 8 | 130 | 250 |
| 7 | 64 | 130 |
| 6 | 32 | 64 |
| 5 | 16 | 32 |
| 4 | 8 | 16 |
| 3 | 4 | 8 |
| 2 | 2 | 4 |
| 1 | 1 | 2 |
What Does 16/14/11 Mean?
A cleanliness code of 16/14/11 means that a 100 ml fluid sample contains:
- Between 32,000 and 64,000 particles larger than 4 microns
- Between 8,000 and 16,000 particles larger than 6 microns
- Between 1,000 and 2,000 particles larger than 14 microns
Multiply these figures by the total volume of fluid within your system and you will begin to understand how clean or contaminated it may be.
Why Does This Matter?
The cleaner the fluid, particularly hydraulic oil, the longer the potential life of pumps, filters and valve chests.
It can also be argued that once hydraulic oil has been properly cleaned and its condition is regularly monitored for wear, there may be no reason to replace it purely on the basis of time in service.
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