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1 1 t [1 1 1 1 1 n 1.3.6 Low Velocity Screens - Fixed 1.3.6.1 Cylindrical Characteristics. The cylindrical screen is a fixed screen consisting typically of a wedge-wire type mesh which was initially designed for liquid/solid separation, not fish exclusion. The screen can be attached directly to a pipe or multiple screens can be attached to a manifold or tower (Figure 1-6). Debris is flushed from the screen surface by a compressed air backwash system. Design screen approach velocities range from approximately 0.3 to 2 ft/sec and are distributed uniformly across the screen surface. Typical Existing Applications. The cylindrical screen is most applicable to submerged pipe inlets for water supply systems. It has also been used successfully to exclude fish from entering the penstock at the Arbuckle Mountain Hydra Facility, near Redding, California. Typical Advantages • Operates well under ice conditions • No electrical or mechanical parts (except for the ancillary pneumatic cleaning system) • Available with openings down to 0.5 mm to exclude organic materials as small as eggs and larvae • Virtually no maintenance of screen required • No debris handling is required • Can operate at velocities up to 2 ft/sec and flows up to 500 cfs f Typical Disadvantages • Not applicable to spillways • Requires large screen area to flow ratio • Not normally designed for flow rates >500 cfs • Compressed air debris backwashing required • Does have some depth limitations Application to Limiting Downstream Passage. Excellent for low to medium flows through primary outlet pipes in submerged applications where flow can approach from almost any direction. Control Structure Feasibility Evaluation Miller Ecological Consultants, Inc., February 18, 1997 1-17