New ISO12500 standards help users compare compressed air quality and contamination

The International Standards Organisation (ISO) has long concerned itself with compressed air quality standards, introducing a series of standards covering the issue back in 1991. Composed of nine parts, they provide quality classifications for the main compressed air contaminants as well as methods to accurately test for the contaminants.

The primary document of the series is ISO 8573.1, which uses a series of purity classifications to define the maximum amount of contamination allowable per cubic metre of compressed air.

For many years, manufacturers of compressed air purification equipment have used the purity classifications of ISO 8573.1 to rate the delivered air quality of their products, and presenting product data in this way should allow users to make easy comparisons about the performance of purification products from different manufacturers. Unfortunately, the ISO 8573 test methods were primarily developed to verify air quality in a compressed air system, not to test purification equipment, therefore not all products claiming compliance with the standards are tested in an identical way.

To accurately detect and measure contaminants in a compressed air system and show compliance with the selected purity levels from ISO 8573.1, the equipment and methods shown in ISO 8573 parts 2 to 9 must be used. These test methods can also be used to test the performance of purification equipment; however, for this purpose, they contain a major omission — one which makes comparison and selection of compressed air filters extremely difficult, if not impossible, for the user.

The vital piece of information which is missing when testing products is an inlet challenge concentration. So even though different manufacturers claim their products meet a certain purity class, they will most likely have been tested with differing inlet concentrations of contamination entering the product. Because challenge concentrations are rarely included in technical data, filter performance that may look similar or even identical on paper can provide significantly different results when installed in a compressed air system.

The ISO 8573 air quality standards were introduced to assist, not confuse, compressed air users, so to overcome the problems associated with product selection, a new standard has been introduced to complement the existing ISO 8573 series.

The new standard, ISO 12500, will consist of three parts, with ISO 12500.1 covering the testing of compressed air coalescing filters for oil aerosol (liquid) removal, ISO 12500.2 to determine the adsorption capacity of oil vapour removal filters and ISO 12500.3 covering the testing of solid particulate filters. Parts one and two were released in June 2007, with part three to follow.

Coalescing filters are probably the most important items of purification equipment in a compressed air system as they are designed not only to remove aerosols (droplets) of oil and water, but also to remove solid particles and microorganisms. For this reason, 'ISO 12500.1 — Testing of Coalescing Filters' is of utmost importance.

ISO 12500.1 has introduced two challenge concentrations of oil aerosol to be used when testing coalescing filters — 40 mg/m³ and 10 mg/m³. The new standard requires filters to be tested using the existing test method and equipment shown in ISO 8573.2 while using one of the two challenge concentrations.

In addition to this, ISO 12500.1 requires filters to be "wetted out", which is representative of an operational filter. Recording of the filter’s initial saturated pressure drop has also been included, again to give a more accurate and representative indication of the filter's operational costs.

Three examples of each model requiring validation must be tested and each tested three times. Published performance data is then based on calculating an average of all the tests in order to provide the person selecting a new product with a more representative indication of performance. This is a big step in the right direction.

*John Davis is Australasian business development manager for Parker domnick hunter
www.domnickhunter.com