Illinois Administrative Code
Title 35 - ENVIRONMENTAL PROTECTION
Part 370 - ILLINOIS RECOMMENDED STANDARDS FOR SEWAGE WORKS
Subpart F - PRELIMINARY TREATMENT
Section 370.610 - Screening Devices

Clear openings for manually cleaned screens between bars should be from 1 to 1 3/4 inches. Design and installation shall be such that they can be conveniently cleaned. An accessible platform shall be provided on which the operator may rake screenings easily and safely. Suitable drainage facilities with return flow to process shall be provided for the platform.

Clear openings for mechanically cleaned screens may be as small as practical to assure the proper operation and maintenance of treatment facilities. Mechanical screens shall be located so as to be protected from freezing and to facilitate maintenance.

For manually or mechanically raked bar screens the maximum velocities during peak flow periods should not exceed 2.5 feet per second. The velocity shall be calculated from a vertical projection of the screen openings on the cross-sectional area between the invert of the channel and the flow line. Excessive head loss through the screen, which may affect upstream flow measurement or bypassing, shall be taken into account.

The screen channel invert shall be at least 3 inches below the invert of the incoming sewers. To prevent jetting action, the length and/or construction of the screen channel shall be adequate to reestablish hydraulic flow pattern following the drop in elevation.

Manually cleaned screens should be placed on a slope of 30 to 45 degrees with the horizontal.

All mechanical units which are operated by timing devices should be provided with auxiliary controls which will set the cleaning mechanism in operation at predetermined high water marks.

Automatic controls shall be supplemented by a manual override.

Electrical fixtures and controls in enclosed places where gas may accumulate shall comply with the National Electrical Code requirements for Class I, Group D, Division I locations.