The DynaSand filter is based on the counterflow principle. The water to be treated is enters through the inlet distributor in the lower section of the unit and is cleaned as it flows upwards through the sand bed, prior to discharge through the filtrate outlet at the top. The sand containing the entrapped solids is conveyed from the tapered bottom section of the unit, the water on the other hand is in slow, constant upward movement. Cleaning of the sand commences in the pump itself, in which impurities are separated from the sand grains by the turbulent mixing action. The contaminated sand spills from the pump outlet into the washer labyrinth where it is washed by a small countercurrent flow of clean water.
The separated solids are discharged through the wash water outlet, while the grains of clean sand are returned to the sand bed. As a result, the bed is in a slow, constant downward motion through the unit. Compressed air for the sand pump is provided via the control panel. Thus water purification and sand washing both take place continuously, enabling the filter to remain in service without interruption.