Sand and accumulated solids are continuously removed from the bottom of the filter and transported to the washbox for cleaning and separation by means of an airlift

This pump consists of a vertical pipe, open at both ends, with the lower end submerged at the bottom of the filter bed. Compressed air is introduced near the bottom of the pipe at a rate of 2 to 5 scfm at 35 psi. This reduces the density of the mixture relative to the outside of the pipe, and causes the mixture to rise to the top where it is discharged into the washbox.

By properly combining the pipe size and the air flow, sand is transported up the airlift with sufficient turbulence to scour waste solids from the sand. For most applications, the sir rate is designed to provide a sand bed turnover rate of every 4 hours or greater. The air flow rate can easily be adjusted based on specific site conditions.