ISO 12669规定了一种确定液压系统所需清洁度水平的方法，即根据液压系统的单独要求，确定工作液压系统的最合适的流体清洁度水平。 它适用于流体清洁度等级按照ISO 4406表示的系统，尽管可以转换为其他污染编码系统。 它既适用于高压和低压流体动力系统，也适用于润滑系统。 它不包括液压流体热分解产生的软变形颗粒的影响。

ISO 12669 specifies a method of determining the required cleanliness level of a hydraulic system, that is, the most appropriate fluid cleanliness level for an operating hydraulic system based upon the individual requirements of that system. It is applicable to systems where the level of fluid cleanliness is expressed in accordance with ISO 4406, although conversion to other contamination coding systems is possible. It is applicable to both high and low pressure fluid power systems and also lubrication systems. It does not include the effects of soft deformable particles that can be generated by thermal decomposition of the hydraulic fluid.