The cleanliness classes according to ISO 4406, important for oil cleanliness!
Oil purity according to ISO 4406: 20/17/14
You may have read this in your hydraulic system manual or on product data sheets, but what does it actually mean?
The cleanliness of the oil is usually important Purity classes ISO 4406 is given as a composite number, such as 20/17/14. The first number refers to particles >4µm, the middle number to particles >6µm and the right-hand number to large particles >14µm.
This means that 100ml of oil with purity class 20/17/14 may contain the following number of particles:
>4µm 500,000 to 1,000,000 (20)
>6µm 64,000 to 130,000 (17)
>14µm 8,000 to 16,000 (14)
(The purity class 20/17/14 is recommended by Argo-Hytos for proportional valves at a pressure of 160-210bar)
Below is the complete table of purity classes according to ISO 4406
| Number of particles from | to | Atomic number |
| 250.000.00 | 0 | >28 |
| 130.000.000 | 250.000.000 | 28 |
| 64.000.000 | 130.000.000 | 27 |
| 32.000.000 | 64.000.000 | 26 |
| 16.000.000 | 32.000.000 | 25 |
| 8.000.000 | 16.000.000 | 24 |
| 4.000.000 | 8.000.000 | 23 |
| 2.000.000 | 4.000.000 | 22 |
| 1.000.000 | 2.000.000 | 21 |
| 500.000 | 1.000.000 | 20 |
| 250.000 | 500.000 | 19 |
| 130.000 | 250.000 | 18 |
| 64.000 | 130.000 | 17 |
| 32.000 | 64.000 | 16 |
| 16.000 | 32.000 | 15 |
| 8.000 | 16.000 | 14 |
| 4.000 | 8.000 | 13 |
| 2.000 | 4.000 | 12 |
| 1.000 | 2.000 | 11 |
| 500 | 1.000 | 10 |
| 250 | 500 | 9 |
| 130 | 250 | 8 |
| 64 | 130 | 7 |
| 32 | 64 | 6 |
| 16 | 32 | 5 |
| 8 | 16 | 4 |
| 4 | 8 | 3 |
| 2 | 4 | 2 |
Which filter fineness is used to maintain the cleanliness class depends on various factors; the most sensitive component in the hydraulic system is usually decisive for the choice of filter medium and filter fineness.
Depending on the application and system component, both component and filter manufacturers have corresponding specifications or overview tables. For example, the manufacturer of proportional valves recommends a filter fineness of 8 to 12 μm (β=200). The manufacturer of filter elements and filter systems recommends a filter fineness of 10µm to maintain purity class 20/17/14.
We will cover the additional details that need to be taken into account when selecting filters and filter elements in another article.
Praise, criticism or questions?
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lars.benk@schuhmacher-tech.de ; +49 7424/9495-663
Lars Benk: Profile of a field-tested expert
Basic training: Tool mechanic, specializing in stamping and forming technology.
Further training: State-certified technician with a focus on mechanical engineering.
Additional qualification: Degree in technical business administration, combining technical know-how with business expertise.
Professional experience: More than a decade of active work in the field of hydraulics.
Specialization: Certified specialist in oil analysis (MLA II – Machine Lubrication Specialist), with a specific focus on the maintenance and optimization of machines through professional lubricant analysis. Certified specialist for hydraulic fluids – specialist knowledge for optimal hydraulic systems.
