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Comparison of Hydraulic Fluid Cleanliness Standards

Hydraulic cleanliness is an important aspect to be considered when specifying hydraulic systems and components, e.g. valve actuators. It is usual to request that the system is flushed to achieve a specific degree of cleanliness, e.g. NAS 6. Measuring hydraulic cleanliness is not straight forward, consequently various standards exist on this subject - see our page on Hydraulic Fluid Cleanliness for a review of the 2 most common.
 
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The ISO Cleanliness Code, ISO 4406, 1987 is the perhaps the most widely used International standard however the dated NAS 1638 standard is still widely quoted by industries involved in UK North Sea.
 
Inevitably, there is a requirement to be able to compare these cleanliness classification codes. The table below gives a good approximation;
 
ISO CodeNAS Class
23/21/1812
22/20/18--
22/20/1711
22/20/16--
21/19/1610
20/18/159
19/17/148
18/16/137
17/15/126
16/14/12--
16/14/115
15/13/104
14/12/93
13/11/82
12/10/8--
12/10/71
12/10/6--


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