Filter class

It is important to be aware of the filter s properties in different environments. Figure 9.2 shows how, in the case of new filters, separation varies with particle size and filter class. The filter class is based on the average efficiency, and a new filter normally has much lower initial efficiency. In the case of electrostatically charged filters, separation may be significantly higher for new filters. The figure should be seen as an indication of minimum separation during actual operation. 

Measures undertaken to improve the indoor air quality (lAQ) have the same effect by upgrading the filter class, increasing the air change rate, etc. These small improvements have grown both in number and in size, little by little. 

Filter class A certain range of filter performance characteristics as specified by international standards. 

Note The filter classifications referred to above relate to the EN1822 and EN779 test standards (EN 779 relates to filter classes G1 to F9 and EN 1822 relates to filter classes H10 to U16). 

Filter classes should always be linked to the standard test method because referring to actual filter efficiencies can be very misleading (as... 

This figure gives a rough comparison between the different filter standards (filter classes should always be connected to the standard test method). 

Section 6.9). The filters for coarse dusts (see Fig. 6.33a), which are quite commonly used in some industrial sectors, do not meet the general requirements for respiratory devices therefore they are not to be used against hazardous particles. Whereas particle filters of type PI and FFPl are not to be used for protection against aerosols, the higher filter classes can be used against fog and droplet-aerosols. 

The standard gas filters (types A, B, E, and K) are subdivided into three classes. Depending on the gas filter class, different maximum gas concentrations are allowed (see Table 6.24). In contrast to particle filter classes, the gas filter classes do not differentiate between rates of leakage. In principle, class 3 gas filters do not have better retention behavior, but have better retention capacity than class 1 filters. 

The most important parameter for gas filters is the retention capacity. The classification into gas filter classes 1, 2, or 3 (see Table 6.24) is rather rough and does not allow a quantitative statement on the service hfe at a given concentration. A breakthrough by the pollutant gas has happened when it can be detected behind the filter at a relevant concentration. 

The labeling of combined filters gives information on the gas filter class and the protection level against particles. For example, a combined filter having the mark... 

In air and liquid filtration, the air segment is more important today. Government regulations and the capability to form composite fabrics with melt-blown layers (if required, with different fiber diameters) are driving the development of air filtration. Composite Media for Heating, Ventilation and Air Conditioning (HVAC) are used in filter classes EU 7 to EU 9 (DIN 24 185). 

In order to remove radioactive substances potentially present in the air flow, most of the ventilation systems are equipped with filter units consisting of high-efficiency particulate filters (HEPA filters, class S) and iodine adsorbers (activated charcoal, KI impregnated). These filters are monitored, either continuously or at regular intervals the filter efficiency of the iodine adsorbers is determined by taking charcoal samples from the filter beds at regular intervals and analyzing them in the laboratory (see Section 6.2.1.5.). 

Filter alignment Categorization of a filter according to the shape of the frequency response also called filter class. 

DQPSK 3MQAM 4MQAM 12PM3 k/4. shift DQPSK with a = 0.35 raised cosine filtering Class 3 Quadrature Amplitude Modulation Class 4 Quadrature Amplitude Modulation 12 state PM with 3 bit correlation IS-54 TDMA voice and data... 

According to the particle size distribution a more-or-less small fine dust is moved towards the filter unit which is located at the top, below the vacuum source. The filter unit should achieve a high separation rate (dustless conveying) whilst maintaining the pressure difference low. With modern filters the exhaust air from the vacuum pump can be blown in the environment whereas with toxic, potent or cancerous powders further treatment is necessary. Precise demands are given by filter classes, for example from BIA [5] (German employer s liability insurance association) or other authorities (Table 17.1). 

Specifically, a basic question to be answered is whether prefilters (primary, relatively coarse filters), EUROVENT Classes EU1-EU4, are suitable on their own, or need to be backed up by fine (second-stage) filters. Classes EU5-EU7, at additional cost. Prefilters normally only remove dust particles down to the order of 5 pm. Applied to centrally heated offices and similar buildings, the amount of fina- dust particles ronaining in the air after a prefilter can be considaable, calling for intalor cleaning or ledecoration at relatively short intervals, typically on a two to three year cycle in urban areas. 

Filter group Filter class Minimum MPPS efficiencies (%)... 

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