ISO (International Standards Organization) is the world’s largest developer and publisher of international standards. There are three ISO standards that relate to compressed air quality and testing — ISO8573 Series, ISO12500 Series, and ISO7183 Series. The most commonly used standard is the ISO8573 Series, in particular, ISO8573-1:2010.
ISO8573 is the group of international standards relating to the quality (or purity) of compressed air. There are nine parts to the standard. ISO8573-1 (part 1) is the most commonly used and relates to quality classifications for compressed air. Parts 2 - 9 specify methods of testing for a range of contaminants.
Here, we will discuss six essential factors to consider when using the ISO8573 Series Part 1 to maximize the effectiveness and efficiency of air treatment in your industrial manufacturing facility.
1. Understanding the air purity classification tables
ISO8573-1 contains air purity classification tables that will provide you with guidance that specifies the minimum air purity required at each usage point, based on the types of contaminants you may seek to remove: solid particulate, water and total oil. See figure 1. From this table you can:
- Specify the amount of contamination allowable at specific points-of-use.
- Identify compressed air equipment specifically designed to meet the purity level you desire.
- Classify, through testing, the actual purity of the compressed air at points of use before and after installation of treatment equipment.
Figure 1 - Combined ISO8573-1 Table
2. Specifying air purity using purity classes
In the ISO8573-1 table, compressed air contaminants are grouped as solid particulate, water and total oil. There are various degrees of each of these contaminants itemized to help in the selection of an appropriate combination of levels, based on your usage. These combinations are referred to as purity classes. When using ISO8573-1 to define the air purity required, it should be written in the following way:
- Write the standard (ISO8573-1).
- Specify the year (revision) stated.
- State the purity classes required (each separated with a colon), e.g. ISO8573-1:2010 [A:B:C:].
- A = the purity class for particles B = is the purity class for humidity (vapor) and liquid water C = the purity class for total oil (aerosol, liquid and vapor).
Below is an example of an air purity specification:
ISO8573-1:2010 Class 1:2:1
Based on figure 1, this air purity specification would specify Class 1 particulate levels not to exceed 20,000 particles in the 0.1 to 0.5 micron size range, with additional levels at other particle sizes; Class 2 water levels identifying a pressure dewpoint (PDP) of -40 degrees Celsius, and Class 3 oil of no more than 0.01 mg of total oil.
3. Facts and myths of ISO8573-1 Class 0
In 2010, ISO8573-1 was updated with the inclusion of Class 0 to the three contaminants. See figure 2. Class 0 was introduced as a “customizable” specification that users and equipment manufacturers could use to identify a specific air quality that would be more stringent than Class 1. This has led to certain misrepresentations or myths. These include:
- Class 0 compressed air is free of all contamination.
- Class 0 is in reference to oil contamination only.
- A Class 0 compressor guarantees oil-free compressed air.
- The Class 0 oil contamination value equals 0 mg/m3.
The following are the important facts to remember:
- Class 0 does not indicate that there is no contamination present.
- Class 0 does not indicate oil-free compressed air.
- A Class 0 compressor does not guarantee oil-free compressed air.
- Class 0 is not in reference to oil contamination only.
- A Class 0 specification must be cleaner than the corresponding Class 1 contaminant specification.
Figure 2. 2010 Classification Table (combined)
4. Which ISO8573-1 revision should I use?
Of the three revisions — 1991, 2001, and 2010 — 2010 should be used when specifying a new system or upgrading a new system. However, if a previous revision has been used to specific purity levels, it is acceptable to continue using it, noting that changes in contamination levels require different purity equipment.
Parker, for example, offers a range of purification equipment that allows the user to specify the quality of compressed air for every application, from general-purpose ring main protection, through to critical clean dry air (CDA) point of use systems. Parker has comprehensive ranges of purification equipment available to exactly match system requirements, ensuring both capital and operational costs are kept to a minimum. Figure 3 provides an overview of Parker purification equipment required to meet or exceed the ISO8573-1:2010 classifications.
Figure 3. Overview of Parker purification equipment that meets or exceeds ISO8573-1:2010 classifications
5. Simple guidelines for selecting purity equipment
Identify the quality of compressed air required for your system. Note that each point in the system may require a different quality, depending on the application. Refer your supplier to the quality classifications shown in ISO8573-1.
- Clearly indicate to suppliers that ISO8573-1:2010 is the edition of the standard you are targeting.
- Make sure the equipment you select will provide air quality in accordance with ISO8573-1:2010.
- When considering coalescing filters, confirm they have been tested to ISO12500-1 and ISO8573-4 standards.
- Ideally, a supplier should provide you with third-party validation of product performance.
- A supplier should provide you with a written guarantee of delivered air quality.
- Oil-free compressor installations require the same filtration considerations as oil-lubricated compressor installations.
- Make sure pressure losses are stated as saturated.
- Verification of blockage characteristics of the filter is helpful when calculating energy costs.
- Be sure to look at the total cost of ownership for purification equipment, not just the initial purchase price.
6. Cost-effective system design
To maximize the return on investment in purification equipment, it is recommended that compressed air is treated for plant distribution in the compressor room to meet the broad needs of the facility. Point of use purification should also be employed with specific attention to the air quality required at each application. This approach assures the air is not over-treated and provides a cost-effective solution to high quality compressed air. Figure 4 shows an example of general purpose air with oil-free air for critical applications.
Figure 4. General Purpose Air with Oil-Free Air for Critical Applications
For examples of cost-effective system designs as well as comprehensive information on ISO8573, including detailed application tables, download the full white paper
This article was contributed by Mark White, compressed air treatment applications manager, Parker Gas Separation and Filtration Division EMEA
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