ABSTRACT
Figure 5.1 shows a bar rack and a traveling screen. Bar racks (also called bar screens) are composed of larger bars spaced at 25 to 80 mm apart. The arrangement shown in the figure is normally used for shoreline intakes of water by a treatment plant. The rack is used to exclude large objects; the traveling screen following it is used to remove smaller objects such as leaves, twigs, small fish, and other materials that pass through the rack. The arrangement then protects the pumping station that lifts this water to the treatment plant. Figure 5.2 shows a bar screen installed in a detritus tank. Detritus tanks are used to remove grits and organic materials in the treatment of raw sewage. Bar screens are either hand cleaned or mechanically cleaned. The bar rack of Figure 5.1 is mechanically cleaned, as shown by the cable system hoisting the scraper; the one in Figure 5.2 is manually cleaned. Note that this screen is removable. Table 5.1 shows some design parameters and criteria for mechanically and hand-cleaned screens.
