A Self Cleaning Autonomous Valve-less Gravity Sand Filter comprises a vertical steel tank divided into a backwash storage compartment, a filter-bed compartment and a filtrate collection compartment.  It operates without any outside energy supply and the water is clarified through the process of sand filtration.  Backwashing occurs on the increase of head principle.  The design eliminates the need for backwash pumps and valves.

The backwash storage compartment is designed to hold an adequate amount of backwash water.  It always fills to the same height, thus providing a constant backwash volume.  Also, as the level of water in the backwash compartment drops, the backwash rate diminishes, so that the backwash rate actually starts at about 44 m/h and gradually slows down to 30 m/h at the end. 

Extensive experience with this diminishing backwash rate has indicated it to be completely satisfactory for cleaning the filter bed.  The high initial flow rate provides greater initial turbulence to wash the sand.  The lower flow rate at the end of backwashing permits the bed to settle evenly and smoothly.

The filter-bed compartment contains fine filter sand.  Unique filter nozzles uniformly collect the filtered water and distribute the backwash water without the need for any gravel layer.

The unit operates under 1,2 to 1,5 meters head loss. Experience has shown that under these conditions, a surface wash and/or an air backwash is not required to break the surface mat to achieve effective regeneration of the filter bed.