What are the recommended flow velocities for sewage screens?

Velocity through the screen openings should be 0.6-1.0 m/s at average flow, while the approach channel velocity should be 0.45-0.9 m/s (Clause 5.2.1 and Table 2).

What is the difference between a coarse and a medium screen?

Coarse screens have clear openings of 50 mm or more, while medium screens have clear openings between 20 mm and 50 mm (Table 1).

What is the typical inclination for a manually cleaned bar screen?

Manually cleaned screens are typically installed at an inclination of 30 to 60 degrees with the horizontal to facilitate raking (Clause 5.4.1).

What formula is used to calculate head loss through a screen?

The head loss (h) can be calculated using the formula h = (V² - v²) / (2g * C), where V and v are velocities through the screen and channel respectively, and C is an empirical coefficient (Clause 5.3.1).

IS 6280

: 1971

sewage screens

CurrentSpecializedCode of PracticeBIMEnvironmental · Public Health Engineering

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This standard provides recommendations for materials, design criteria, construction, installation, and operation of sewage screens. It covers various classifications of screens (coarse, medium, fine) and outlines key hydraulic design parameters like flow velocities and head loss for both manually and mechanically cleaned screen types used in wastewater treatment.

sewage screens

Quick Reference Values

Velocity through screen bars at average flow0.6 to 1.0 m/s

Velocity through screen bars at maximum flowNot exceeding 1.2 m/s

Velocity in approach channel (min)0.45 m/s

Velocity in approach channel (max)0.9 m/s

Inclination of manually cleaned bar screens30 to 60 degrees from horizontal

Inclination of mechanically cleaned bar screens0 to 30 degrees from vertical

Clear spacing for coarse screens50 mm and above

Clear spacing for medium screens20 to 50 mm

Key Formulas

h = (V² - v²) / (2g * C) — Head loss through screen, where V is velocity through screen, v is approach velocity, and C is a coefficient of discharge.

Practical Notes

Ensure the approach channel is straight for a sufficient length (typically 8-10 times the channel width) to ensure uniform flow velocity distribution before the screen.

The design must account for the handling, drainage, and disposal of collected screenings, which is a critical operational aspect.

For mechanically cleaned screens, redundancy (e.g., a standby unit or a manual bypass screen) is highly recommended to allow for maintenance and handle breakdowns.