Know how


Filter classifications:

Filter classifications serve the comparability and standardization of qualities.

Licensed test institutes  are allowed to run this standardised tests and to write attests to prove achievement of filter class.
It is to be noticed that with these standardised tests the real  praxis relations can be copied only roughly. It is not possible to draw a reliable conclusion out of this test results.
To get clear results for filter life time, pressure drop, filter efficiency  etc. – comparison tests in praxis are necessary.
To guarantee the optimum, filtex® offers for each filter class different filter products, various product lines and special filter types.
There are different classification test standards for the air filters, liquide filters, e.g..
The commonly used classification  standard can also vary from different industries or regions.

Following organisations are developing classification standards for air filters:

  • ISO: International Organisation of Standardisation
  • ASHRAE: American Society of Heatin , Refrigeration and Air-Donditioning Engineers
  • IEST: Institute of Environmental Sciences an Technology
  • UL: Underwriters Laboratories

Coarse dust and fine dust air filter:

The international standard is the standard EN779 for the filter grouping of coarse dust filters and fine dust filters (G2-F9).

In a test channel the filter becomes dusted with  standardised test dust, until a defined final pressure drop is reached(250Pa for G2 – G4, 450Pa for F5 – F9).  The everage value of filter arrestance/efficieny gives the filter classification.

EPA/HEPA/ULPA air filters:

Filters for Clean room conditions, class E10(H10)-U17 are classified according standard EN1822.
The filter class is no average value.  The high filtration efficiency is guaranteed from the beginning.

A classification attest is made for each filter. The filter is fed with standardised test aerosol DEHS. The number of passing particles are counted on the filter air outlet side by use of a scanner.

The filtration efficiency is determined about the passage grade of the MPPS. (Most Penetrating Particle Size, in the size between 0.1 and 0.3ym) (for more information see register “CLEAN ROOM TECHNOLOGY”)


Dust filter - dust removal machines:

The filters are distinguished after use-categories (U, S., G, C...).
The category is an index for the max.workplace concentration that may be reached by use of this filter  (MAK value)

The MAK value is the middle workplace concentration, defined as a middle concentration of a pollutant (in milligramme) in the air (in cubic metres) in the workplace (mg / m ³)

Dust removal machines must be checked and certified  from legal institutions  (eg.: BIA in Germany)

Foam filters:

The fineness of  foam filter is usually stated by the specification of PPI (Pores by Inch).
60PPI means 60 pores on 25.4 mm


  • Fleece filter, liquid filters, industry filters:

    The fineness of industry filters, fleece filters and liquid filters is usually stated by the specification of the pore sizes (passage size in ym).
    Besides special application qualities can be of  importance.