PURIFYING COMPRESSED air is a key step in most manufacturing applications, as contamination can damage pneumatic tools and components, create product quality issues, and lead to failed inspections and unexpected downtime.

ISO 8573-1 is the international standard for compressed air purity, and defines compressed air quality in three contaminant categories. For each contaminant category, ISO 8573-1 assigns a class number based on either particle concentration per size bin (particles), pressure dew point (water) or total oil concentration (oil), with a lower class number corresponding to a more stringent contaminant limit. 

Maintenance support

Specifying compressed air against a defined ISO 8573-1 class enables a shift from reactive intervention to condition-based maintenance.

Each contaminant category in ISO 8573-1 contributes to different failure mechanisms, although effects often interact in practice. Particulate classes are selected based on downstream sensitivity, ranging from general pneumatic applications (typically Class 2–3) to more critical instrumentation and actuation systems (potentially Class 1).

Moisture-related failures depend on the pressure dew point relative to the lowest temperature in the system. ISO 8573-1 defines dew point classes which are used to specify and verify dryer performance. Oil contamination can affect elastomer seals, and can also contribute to deposit formation.

Differential pressure across filter stages is the primary operational indicator for particulate filter loading and is commonly used to schedule filter element replacement. Monitoring pressure drop against manufacturer limits enables planned maintenance and helps avoid both energy losses and filter performance degradation.

Specifying the correct purity class also helps to avoid two opposite economic penalties. Over-specification imposes unnecessary pressure drop, energy cost and element replacement expenditure across the lifetime of the installation, while under-specification generates unplanned repair costs, scrap and quality non-conformities that typically exceed the saving on filtration hardware. The required class must therefore be defined by the end user against application risk. While ISO 8573-1 provides the classification framework, it does not prescribe which class applies to which use case.

Product quality

Maintaining the required purity class turns compressed air from an imprecise utility into a measurable and controllable part of the manufacturing process. The standard’s classification therefore helps manufacturers to confirm that every product batch is exposed to the same level of air purity, helping to remove any compressed air variables that can cause defects. 

Regulatory compliance

ISO 8573-1 is the reference framework used by audit bodies, certification schemes and industry customers to assess compressed air quality. While not legally required in every jurisdiction, it has become the de facto standard across sectors such as food and beverage, pharmaceuticals, medical devices, electronics and automotive. Using this global standard helps remove the guesswork, helping facilities to achieve compliance with it through periodic verification of air quality against the declared class.

Before making changes to a compressed air system, engage with an expert to conduct a comprehensive system evaluation against ISO 8573-1. This will see a transition from assumption-based maintenance to data-driven reliability, helping the production process to be both compliant and cost-effective.

The most critical stage is the gap analysis, where an expert compares an organisation’s measured ISO class against the required ISO class for a specific application, and provides a roadmap for optimisation.

Correct dryers and filters

Selecting the correct dryer and filter combination is a balancing act between achieving the necessary air quality and minimising the total cost of ownership through energy and maintenance considerations. 

Dryers should be installed early in the system to reduce moisture before air reaches filters and downstream equipment. A common mistake is to over-specify a dryer, which leads to unnecessary energy consumption. 

Filters address the A (solid particles) and C (total oil) parts of the ISO code. High-efficiency particulate filters are critical at two key points in the treatment chain: immediately after adsorption dryers, where they capture desiccant fines released by the adsorbent bed, and at point of use, where they provide the final barrier protecting sensitive processes and equipment from any residual particulate carry-over from the distribution piping. Without high-efficiency filtration at these stages, an otherwise compliant system can easily fall short of its target ISO particle class.

Coalescing filters are deployed at multiple stages. However, they do not remove oil in vapour form. That requires dedicated activated carbon filtration further downstream. They are installed in the most demanding industries where even trace hydrocarbon vapour can compromise product integrity, contaminate a batch or pose a health risk. 

A common framework for clean air​

With the right combination of dryers, filters, point-of-use protection and ongoing measurement, an organisation can move compressed air from being an unmeasured background utility to a fully characterised, controlled and auditable input to production. Whatever the industry, ISO 8573-1 provides a common global framework that aligns maintenance teams, quality managers, procurement, auditors and executive leadership around a single, measurable definition of "clean air" that delivers consistent product quality and reliable operations – and the ability to prove it.

Louis Cottaz is product manager at Donaldson

For more information: 

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