The feeder is just as important as the hopper above it. To be effective, the feeder must uniformly draw material through the entire cross-section of the bin’s discharge outlet (7). An obstructed outlet, due, for example, to a poorly designed feeder or partially opened gate, will result in funnel flow regardless of the hopper design. Three common types of bulk solids feeders, along with key features required to ensure uniform withdrawal of material from the entire outlet of the hopper, are discussed in the following paragraphs. Screw feeders. These are well suited for use with hoppers that have elongated outlets. Since a screw feeder is totally enclosed, it is good for use with fine, dusty materials. In addition, it has few moving parts, so it requires less maintenance than a belt feeder.