how automatic backwashing works in sand filter?

Answer 1

sand filters are also used for pre treatment of quality water systems drawing from a dirty source. i use sand filters to clarify cooling tower water (remove heavy particles and dust) . the normal flow would be from the top of the vessel to the bottom or a spot near the bottom. the unwanted particles get "trapped" in the sand on the way down, eventually the sand becomes "plugged up" and passages or veins may form in the sand allowing water to pass with little treatment, in an automatic backwash system the system will shutdown or open a bypass line to allow the water flow to now be reversed from the bottom to the top of the vessel, this water then carries the "trapped" partices and is washed away as effluent, the backwash also agitates the sand in an upward flow to reorganize the sand and eliminate any channeling or veining. The systems i have operated were equipped with all automatic water valves, making a backwash as easy as one button to manipulate each valve into the desired position.

Answer 2

A sand filter is used to treat wastewater. When waste water goes through a sand-filter, the sands voids collect particles. When you backwash the particles are essentially purged out of the voids. The purged particles then usually go to a settling/evaporation pond. After backwashing the sand is ready to recieve more particles.

Answer 3

Don't know.