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ISO cleanliness codes are based on International Standard ISO 4406:99. ISO codes show three sets of numbers separated by a slash. These numbers refer to ranges depicting the number of particles larger than 4 micron, 6 micron and 14 micron respectively. Because 6 micron and 14 micron particles are both larger than 4 micron those particles are all also included in the first number. The second number shows particles larger than 6 microns. The last number only shows particles larger than 14 microns.
The table indicates the number of particles in 100mL of fluid that is specified against each number in the range.
(number of particles per 100 mL)*
| Range no. | More than | Up to and including |
|---|---|---|
| 24 | 8,000,000 | 18,000,000 |
| 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 |
A dirty hydraulic oil could have an ISO cleanliness level of 22/20/18.
ISO 22/20/18 |
||
|---|---|---|
| particles size | number of particles | range no. |
| 4µm + | 2,000,000 ≤ 4,000,000 | 22 |
| 6µm + | 500,000 ≤ 1,000,000 | 20 |
| 14µm + | 130,000 ≤ 250,000 | 18 |
