Drum screens are widely used throughout Europe, Asia, and South America in electric power plants and other large water intakes. Drum screens are reliable screening devices utilizing very few moving parts. A double entry drum screen is mounted in a concrete channel with its axis oriented perpendicular to the water's flow. Single entry drum screens, also called cup screens, are similar to the larger double entry drum screens. Flow enters the drum through its open end and exits outward through the wire mesh mounted on the screen's periphery. Another cylindrical screen design utilizes a slowly rotating wire mesh screen with a water backwash spray to prevent accumulations of debris from a pump intake. The revolving disc screen is a simple and compact screening device that is closely related to the drum screen. It consists of a flat disc covered with screening media that rotates about a horizontal axis, perpendicular to the water flow.