Trends in Pleated Cartridge Filters (continued)

Pleat Spacing

You also need to consider the spacing between the cartridge filter's pleats when selecting a filter. For years, one problem with pleated cartridge filters has been tight pleat spacing that prevents the dust building up in the pleats from being easily removed with reverse-pulse cleaning.

Most filters are made with pleating machines that crease the media into an S shape, pinching off the pleat's bottom half (toward the filter's interior), as shown in Figure 4. This pleating method tightly compresses the pleats, leaving much of the media area unavailable for filtering and allowing dust to remain trapped in the filter even after cleaning.

Figure 4 - Tightly compressed pleats (top view)

Filter manufacturers have developed cartridge filters with open-pleat designs to overcome these problems. One type is a spunbonded polyester open-pleat filter with pleats that are dimpled along their vertical length. This dimple prevents adjacent pleats from touching, making more usable media area available and facilitating dust release so that filter cleaning requires fewer pulses and, thus, less energy.

In another type of open-pleat filter, hot-melt separator beads - that is, intermittent beads or dots of hot-melt glue - between pleats on the interior media side form a rigid structure that maintains uniform pleat spacing, as shown in Figures 5a and b. Based on a pleating method developed for manufacturing high-efficiency particulate air (HEPA) filter media for clean rooms, the hot-melt separator beads open up the entire pleat length, enabling the full pleat depth to be used for filtering and allowing higher airflow per square foot of media than older pleating methods. By comparing the pleat spacing shown in Figures 4 and 5, you can see that the filter with hot-melt bead pleat spacing (Figure 5) has more usable media area than the filter with tighter pleat spacing (Figure 4). The greater amount of usable media area allows the filter to hold more dust between cleaning pulses, produces a significantly lower pressure drop, and improves dust release during cleaning.

Figure 5a - Open pleats made with hot-melt separator beads. (Exterior view)

Figure 5b - Open pleats made with hot-melt separator beads. (Interior view)

In addition to considering pleat spacing, be cautious about selecting a cartridge filter encircled with an exterior cage. The cage is meant to help the pleats maintain their shape during reverse-pulse cleaning, but the cage covers some of the pleats' open area and can trap dust, preventing it from leaving the filter during cleaning and potentially shortening the filter's life. To avoid these problems, select a filter that uses cords, bands, or similar devices around the filter. These devices cover much less of the filter's open area and don't trap dust.

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