Backwash pool is the most important maintenance operation for the correct performance of a pool with a granular medium, which can be activated carbon, sand, zeolite, ion exchange resin … or multimedia pool . There are important reasons, and not always detectable to the naked eye, for which it is necessary to backwash the granular pool. Eliminate the solids retained between the granules of the medium.
The amount of these solids will depend on the concentration of suspended solids in the treated water, the size distribution of the same (granular media beds retain solids from a certain size) and the volume of water treated since the last backwash pool. If the aforementioned verification is not made, there is a risk of not being able to expand the bed, or of the coal being dragged out of the adsorber.
In essence, a good backwash pool is one in which two things are achieved: expand the bed by 30 to 40%, and stratify the carbon particles at the end of the operation. To achieve the first, it is necessary to make sure that the bed is expanded, and not simply rely on the graphics reported by the manufacturer. These graphs give an approximate idea of the flows with which different percentages of expansion are achieved, but a final adjustment must be made for each particular case.