Figure 6.3 depicts a typical comminutor. When designing a comminutor, head-loss should be considered. Head-loss through a comminutor is usually in the range of a few centimeters to 0.9 m (3 ft). Therefore, the manufacturer‘s ratings should be decreased by 70 to 80 percent to account for clogging of the screen, since manufacturer‘s head-loss characteristics are usually based on clean water flow (Crites and Tchobanoglous, 1998).
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When a comminution device is installed upstream of a grit removal device, the teeth of the comminutor are subject to high wear and tear. Rock traps are recommended to prolong the life of the comminutor. In addition, a bypass manual bar rack should be installed in the event that flow rates exceed the comminutor capacity or there is a mechanical failure.