ISO 8573-1 Moisture Measurement in Compressed Air

Moisture content and what it means for compressed air quality

In many respects, standards are the foundations that underpin all industrial operations. They create a level playing field that ensures fair competition, while reducing risk and enhancing safety, efficiency and innovation. They also provide the frameworks that help manufacturers develop reliable production processes, with accepted parameters against which performance, reliability and quality can be measured.

For industrial users of compressed air, one of the key standards is ISO 8573. This defines the nature and permissible concentration of contaminants in a compressed air stream. Note that ISO 8573 does not include breathing or medical air; these are covered in separate BS EN 12021 standards and various HTM (Health Technical Memoranda) guidelines.

ISO 8573 was originally introduced in 1991 and has subsequently been updated on a number of occasions; the latest version is ISO 8573:2017. As the International Standards Organisation (ISO) tends to reappraise standards every five years, we should be due for a review in 2022.

The current version of the standards consists of nine parts, with the Part 1 relating to the types of contaminants and different levels, or classes, of purity, while the remaining eight parts cover various test methods and instruments. In full, these are:

  • ISO 8573-1: Contaminants and purity classes
  • ISO 8573-2: Test methods for oil aerosol content
  • ISO 8573-3: Test methods for measurement of humidity
  • ISO 8573-4: Test methods for solid particle content n
  • ISO 8573-5: Test methods for oil vapor and organic solvent content
  • ISO 8573-6: Test methods for gaseous contaminant content
  • ISO 8573-7: Test method for viable microbiological contaminant content
  • ISO 8573-8: Test methods for solid particle content by mass concentration
  • ISO 8573-9: Test methods for liquid water content
  • Contaminants as defined in ISO 8573-1

    For most operational users of compressed air, the most important part of ISO 8573 is Part 1. This defines three groups of contaminants:

  • Group A, particulates
  • Group B, moisture in vapor, aerosol, and liquid forms
  • Group C, oil in vapor, aerosol, and liquid forms
  • For each Group, the standard then categorises different Quality Classes, each with a maximum permissible concentration of contaminants. For example, for Group B, there are 9 Quality Classes, ranging from Class 1, which is the most stringent, to Class 9, the most basic, while for Group A there are seven Classes and for Group C five Classes. These are shown below:

    BCAS-The Filtration and Drying of Compressed Air
    Caption: BCAS-The Filtration and Drying of Compressed Air

    Download BCAS-The Filtration and Drying of Compressed Air.pdf

    It is normal for equipment to be specified in line with these categories. For example, a compressed air filter might offer performance to ISO 8573:2010 Class 1-2-2; i.e. it conforms to Class 1 for particulate filtration, Class 2 for moisture removal and Class 2 for oil filtration.

    Note that in each Group there is a Class 0. This is normally based on an agreed specification between the user and equipment supplier and is set at a level that is suitable for the application and that can be validated using the relevant test criteria stipulated in ISO 8573 Parts 2 to 9.

    Note also that Group A does not include microorganisms, although testing for the presence of these contaminants is defined under Part 7 of the ISO 8573 standard. In applications such as food and beverage, where microbiological contamination needs to be controlled, the normal approach is to define safe criteria based on the demands of the application itself. This can then be controlled by using precise dew-point measurement and air drying, to the level where the growth of microorganisms is inhibited, followed by specialised sterile point-of-use filtration.

    Why ISO 8573 is important

    In common with all industrial standards, ISO 8573 plays an essential role in managing production or process operations. It’s particularly important for maintaining levels of compressed air quality, to protect equipment that is downstream of each compressor. In food or pharmaceutical processes, ISO 8573 will help to protect the condition of the finished product, with regular system testing to the relevant criteria specified in ISO 8753 being an important factor is providing full manufacturing traceability.

    Adhering to the standard will help to simplify the design and operation of compressed air systems, providing a set of recognised parameters against which equipment from different suppliers can be evaluated. It also enables the performance of each system to be optimised, to reduce construction, operation and maintenance costs; for example, the primary compressed air ring-main may be specified to a higher Quality Class, with lower – i.e. more stringent – Quality Classes being applied at specific points in a production line.

    A final, but equally important point, is that the standard can help to minimise energy costs. By having a clear understanding of the exact requirement for the maximum acceptable levels of contamination, especially moisture, it is possible to optimise the performance of systems components such as dryers without affecting air or final product quality.

    This is where our Michell advanced dew-point sensors and transmitters have a crucial role to play, providing real-time monitoring and control of compressed ait systems. We’ve over 45 years of experience in trace moisture measurement, making Michell Instruments the application experts when it comes to controlling moisture in compressed air.

    Our dew point meter ranges from Michell Instruments (our brand) are ideal for spot checking in compressed air systems.

    To learn more, contact us, today to discuss your application.

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