Measuring the performance of air filter media

Measuring the performance of air filter media

Generally accepted test methods exist for fabricated air filter cells in applications ranging from residential air conditioning to nuclear reactor safety systems. Some standards also exist for evaluating dust control equipment using cleanable fabrics and nonwovens in various forms. Test methods for the filtration media used in the filter elements of these systems have been slower to arrive. However, complete test methods for filtration media - analogous to ISO TS 21220 test for fabricated filter cells, for example - are now passing through the international consensus-standards process for both disposable and cleanable filter media.

There are valid reasons for the difference. Device manufacturers are reluctant to reveal the details of media used in their products. The exact mix of fibres, thickness, and other media physical properties are often crucial to the performance of a filtration product. The performance of a pleated filter is not easily predictable from the performance of flat sheet media. The performance of cleanable media is highly dependent on the geometric configuration of the separator device and its cleaning means.

petri dish     string wound filters     active carbon filters

Nevertheless, media test methods are needed for product quality control, and to assure design engineers and users that media will deliver promised performance under the environmental stresses of specific applications. Although some test results, required by government agencies for protecting public health, are openly available, other results can be kept under confidentiality agreements, to protect manufacturer trade secrets, while using rigorous, fully-defined test methods.

A survey of current standards relating to media testing shows that test methods for many media attributes have already been addressed by national and international standards-writing organisations. International standards for media could be built on this experience.

Test standards for filter media, like test standards for filtration devices, fall into two general categories - those intended for disposable filter cells, and those intended for devices having means for cleaning the filter media. The bulk of disposable filters are used in building HVAC systems, clean rooms and other applications having relatively benign environmental conditions. Cleanable media, however, are used in industrial processes, stack-gas cleaning and other applications which may require operation at high temperatures, wet or corrosive gas conditions, and much higher dust concentrations than the other group.

We identify a third category of gas filtration: specialty applications. We discuss these for a few categories: nuclear reactor and fuel-processing safety systems; grease arrestors; paint overspray capture; and mist eliminators and coalescers; metallic fiber media. Filter media for these applications may be identical with those used in the other two groups, but they require different test methods, and demonstration that the mechanical properties of the media can withstand the special environmental conditions of their applications.

SPE Cartridge      Syringe       petri dish     string wound filters     active carbon filters     96 well plates     roller bottle     tissue culture flask