Mechanical components are an essential part of any system, however components such as pins, bearings, and bushes are not immune to the damaging effects caused by friction [1]. To ensure that mechanical components remain operational, it is essential that each part is sufficiently lubricated. Furthermore, taking the amount of lubrication per component into consideration alone is not enough [2], the lubricant must also be clean. Fluid cleanliness is measured using the ISO 4406:21 reporting standard [3], which provides a standardised framework for assessing the cleanliness or contamination levels of lubricants used in machinery.

ISO cleanliness is the standardised method to measure the cleanliness or contamination level in fluids like oils [3]. It is represented by three numbers, such as 21/19/16. Each value corresponds to the number of particles of different sizes contained in 1 millilitre of fluid, representing a specific range of particle count for different particle sizes. The first number measures particles larger than 4 microns, the second counts those larger than 6 microns, and the third tracks particles larger than 14 microns [3]. Lower numbers indicate cleaner oil, which is crucial for machinery performance and longevity.

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ISO Cleanliness Codes:

What causes oil to become dirty?

Oil contamination primarily results from a combination of factors, with human interaction as a predominant contributor [4]. When individuals engage with machinery, whether through standard operation or maintenance, they introduce contaminants like dust and debris into the fluid. Simultaneously, friction and abrasion between machinery components generate tiny metal and material particles that further compromise oil cleanliness. These microscopic particles pose a significant threat to the oil’s purity. Moreover, exposure to moisture and chemical reactions can lead to metal corrosion, which introduces additional impurities into the oil [4]. Consequently, even seemingly clean oil can harbour these contaminants, negatively impacting both the oil’s efficiency and the machinery it lubricates [4].

Figure 1 – Causes of contamination into system

How clean is your oil really?

Misconceptions about oil cleanliness often arise from underestimating how easily it can fall out of specification. Even when oil looks clean, it can hide contaminants that aren’t immediately visible. It is essential to understand that even tiny particles can significantly affect both the oil’s performance and the machinery it lubricates. This concept becomes clear when examining Figure 2, which displays a patch of brand-new oil with an ISO cleanliness code of 21/19/16, and Figure 3, which shows a patch with an ISO cleanliness code of 13/11/09. The significant contrast between these two images illustrates how invisible particles can compromise oil quality.

Understanding the importance of keeping your oil clean in mechanical systems and having reliable measures in place can help minimize downtime, reduce maintenance expenses, and extend the lifespan of your machines. It all begins with a simple question: “Is my oil clean?”

FloSolve is the authorised distributor of PALL equipment. For more information on our range of PALL oil analysis solutions contact us on (+27) 011 389 5300 or


[1] M. Gandelli, “Static and dynamic friction: effects on mechanical components,” 8 September 2023. [Online]. Available:

[2] J. Wright, “Implementing a Best-Practice Lubrication Program,” 8 September 2023. [Online]. Available:

[3] N. Corporation, “What is the ISO Cleanliness Code,” 8 September 2023. [Online]. Available: [Accessed 8 September 2023].

[4] Noria Corporation, “3 Ways Contaminants Can Enter Lubrication Systems,” Machinery Lubrication, [Online]. Available: [Accessed 5 October 2023].

[5] J. Fitch, “Hey, Aren’t machines supposed to wear out,” Noria, [Online]. Available:’s%20third%20reason%20why%20machines,(corrosion)%20and%20mechanical%20damage.. [Accessed 28 September 2023].