Screens:

Screens are provided in front of river/stream intakes so as to remove large size floating material from raw water. There are mainly two types of screen, i.e.

(i) Coarse screens (trash racks) and

(ii) fine screens.

Coarse screens are provided at river/stream intakes to prevent floating material of fairly large size entering into the intake. The bars of steel forming screen are normally of about 25mm diameter and are spaced 100 mm apart. The screen is placed at a slight inclination from the vertical to facilitate raking. Sometimes, bars in the form of frames are placed in duplicate so that one of the frames may be lifted for cleaning or repair when required without hampering the process. The bars in the frame are placed such that velocity of water through the screen opening should not exceed 0.5 m/sec.

Fine screens remove the fine suspended particles, which get pass through coarse screen. This is made up of fine wire or perforated metal with opening less than 10 mm wide. These are normally fitted immediately after the coarse screens.