What does backwash mean in practice?
Water flows from bottom to top, loosens the layer and carries the accumulated sediment to the drain without losing the proper fraction of the medium.
When does it matter?
Too little flow will not clean the bed, and too much flow may wash out the medium or overload the drain.
Which solutions are related to it?
The flow is selected according to the column diameter, bed density and water temperature, and the expansion is checked during startup.