The circulation system keeps water continually moving from the pool basin through the filtration system, the chemical feeder, the heater, and then back to the pool basin again.
- Circulation – The first key to good pool care (Ronald Parrs)
- The physics of circulation (HubPages)
- Swimming pool main drains and circulation (About.com)
During filtration, dirty water from the pool flows down through filters so that dirt and other insoluble pollutants are captured while the filtered water passes out the bottom of the filter and back to the pool basin. Over time, the debris collected in the filters begins to slow down the water flow. When this happens, the flow of the water can be reversed (called backwashing) so that the debris is pushed out the top of the filters and into the sewer.