The sand washers are delivered to the site as complete products. The sand de-watering conveyor is installed to the unit at the site. A sand washer differs from a sand de-watering unit in that it includes a mechanical propeller mixer used to keep the water in the tank in slow motion so that light organic matter is removed from the tank as overflow.

A sand bed is accumulated to the bottom of the sand washer and flushed automatically with air and water from time to time based on the backwash principle. The washed sand is led out of the unit by the drying spiral conveyor. Sand removal is controlled by measuring the surface level of the sand bed. Washing water is led out of the unit as overflow to the next part of the treatment process.