Types Of Filters

Figures 7.1 to 7.8 show examples of the various types of filters used in practice. Filters may be classified as gravity, pressure, or vacuum filters. Gravity filters are filters that rely on the pull of gravity to create a pressure differential to force the water through the filter. On the other hand, pressure and vacuum filters are filters that rely on applying some mechanical means to create the pressure differential necessary to force the water through the filter.

The filtration medium may be made of perforated plates, septum of woven materials, or of granular materials such as sand. Thus, according to the medium used, filters may also be classified as perforated plate, woven septum, or granular filters. The filtration medium of the microstrainer mentioned above is of perforated plate. The filter media used in plate-and-frame presses and vacuum filters are of woven materials. These units are discussed later.

Figures 7.1 and 7.2 show examples of gravity filters. The media for these filters are granular. In both figures, the influents are introduced at the top, thereby utilizing gravity to pull the water through the filter. Figure 7.1a is composed of two granular filter media anthrafilt and silica sand; thus, it is called a dual-media gravity filter. Figure 7.1a is a triple-media gravity filter, because it is composed of three media: anthrafilt, silica sand, and garnet sand.

Generally, two types of granular gravity filters are used: slow-sand and rapidsand filters. In the main, these filters are differentiated by their rates of filtration.

Influent

Influent

Influent

Influent

FIGURE 7.1 (a) Dual-media filter; (b) triple-media filter.

Effluent (b)

FIGURE 7.1 (a) Dual-media filter; (b) triple-media filter.

FIGURE 7.2 A typical gravity filter.

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