First stage filtration of water is done by Bar Screens (also known as Trash Racks). These remove bulky and coarse material. The spacing of bars on such bar screens depends upon the quality of filtered water required. To prevent material too coarse from reaching the travelling band screens, bar screens may be used in two stages where the first screen with wider bar spacing remove bulky solids; a second bar screen with smaller bar spacing then remove debris still coarse enough to clog travelling band screens installed downstream for finer screening.
Bar screens can be categorized into two types:
- Removable Type
- Fixed Type
In case of removable type, single or multiple segments of bar screens, with the help of a lifting beam, are lowered into or raised out of the intake chamber by means of guides installed on the side walls. The beam lifts out the segments for necessary cleaning of the screens.
In case of fixed type, bar screens, consisting of steel frames of welded design over which flat bar sections are fixed by bolting/welding, are fixed to the bottom of the chamber by grouting/bolting. The flats are suitably spaced to meet design requirements. Interchangeable bar sections are provided for easy replacement. Fixed type bar screens have to be cleaned out by bar screen cleaning equipment.
On the basis of design, differential water head, suitable selection can be made of structural parts, screen bars and supports.
| Cable Operated Bar Screen | Bar Screen with Cleaning Car | Portal Track Trash Rake | |
|---|---|---|---|
| Channel Width | 1000-5500 mm | 1000-5500 mm | 1600 mm |
| Channel Depth | 20000 mm | 20000 mm | 20000 mm |
| Clear Spacing | 15-60 mm | 15-60 mm | 50-100 mm |