ISO 4406, the purity classes and more…
What is behind ISO 4406?
ISO 4406 is a standard, a system for coding the purity of a medium.
Cleanliness classes can be determined and defined using this standard; many manufacturers of hydraulic components and systems use these cleanliness classes to ensure safe and long-term operation of the components and the system.
Further details about the purity classes according to ISO 4406 can be found on our website.
- The cleanliness classes according to ISO 4406, important for oil cleanliness!
- Oil purity according to ISO 4406 18/16/13…how do I achieve this? Recommended filter ratings
Information on the cleanliness classes of components and systems can be found in the manual or on the manufacturer’s data sheets.
Filter finenesses are usually also recommended for operating the system, e.g. 3µm, 5µm, 10µm, etc.
Why is compliance with these purity classes so important?
As already mentioned, manufacturers usually specify cleanliness classes according to ISO 4406 for hydraulic components, machines and systems. If necessary, filter finenesses are also specified in µm (micrometers).
These specifications are determined or selected taking into account the individual, system-relevant components. For example, depending on the manufacturer, there are recommendations for the purity class to be used for a wide variety of components.
You can find an overview of this in this article, among others.
- Oil purity according to ISO 4406 18/16/13…how do I achieve this? Recommended filter ratings
For example, a purity class according to ISO 4406 with the code 18/16/13 with a filter fineness of 5µm is recommended for a proportional valve (depending on the manufacturer). If you now look at the code 18/16/13 in ISO 4406, you come to the following conclusion (based on 100ml):
| Purity classes according to ISO 4406 | Number of particles from | to |
| 18 – (Partikelgröße > 4µm) | 130.000 | 250.000 |
| 16 – (Partikelgröße > 6µm) | 32.000 | 64.000 |
| 13 – (Partikelgröße > 14µm) | 4.000 | 8.000 |
If the purity of the oil is in the range 18/16/13, there should be no unplanned defects or excessive wear on the proportional valve in question.
However, if the purity class is not adhered to and is significantly worse, for example 21/19/16 (the higher the atomic number, the more particles in the oil), this leads to increased wear and the piston in the proportional valve can jam.
The “gap” between the piston and the piston housing is only a few micrometers wide; particles collect here and under pressure this leads to abrasion and chipping on the control edges. The control quality of the valve steadily decreases, the friction forces between the piston and the piston housing increase and sooner or later the piston “eats” and jams. The valve is defective and needs to be replaced.
Most of the time, this is a gradual process that you only notice during ongoing operations when it is too late.
Who ensures compliance with the purity class?
If you do not have a maintenance contract with the manufacturer or service provider for your system/machine, you should take care of it yourself.
Is there a maintenance contract? Then you should check whether “oil care” is also part of the service. It is particularly important that this oil care is carried out regularly and documented! Otherwise, if there is a defect, you will have no idea what condition the (hydraulic) oil is in or you will not see any trend.
Is the pump defective due to its age? Or did chips and other contamination lead to an early defect? In the event of a warranty claim, this is of central importance.
What options are there to monitor the purity of the oil?
Depending on the plant/machine or system, there are various ways to monitor cleanliness.
Starting with the regular oil test that you can do, for example Oil check can be analyzed by using one or more Sensors , to portable Oil diagnostic devices and particle counters There are a variety of providers and options.
Alternatively, there are also service providers who can take on this task for you.
No matter what you do, it’s important that you do something!
Simply letting it run and changing the oil every now and then is not the best solution.
We have dedicated a separate article to the topic of oil changes:
How can I clean the oil?
Have you determined through the oil analysis that the required purity cannot be met?
Then you should act quickly! Perhaps system-relevant components have already suffered damage.
- Ask: Why is the installed filtration not enough?
- Ask: I can with one Oil service device Clean the oil or do I need to change the oil?
- Ask: How can I ensure that the oil is cleaned better in the future and permanently meets the required purity class?
This question is too complex and the systems on the market are too different to be able to give a general answer.
So it is more than just a cleanliness class according to ISO 4406…
In my opinion, ISO 4406 is the basic framework, the basis on which we can orientate ourselves and move along. However, it is of course used by the manufacturers as a default, and rightly so.
What you then do with the results of the oil sample or the reports from the sensors varies from case to case.
It is important to be informed, take care and sharpen your senses for this topic.
It’s about extending the oil usage time, the service life of components and machines, costs and, last but not least, the resulting environmental influences.
My advice to you is to take the topic seriously, take care of it or use external expertise!
Lars Benk – “Oil care with passion”
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.
