The filters in this system are high-rate sand filters. Sand filters consist of a large tank, which is usually made of a polyester/fiberglass mix but can also be made of polyethylene, stainless steel or other materials depending on the application. During filtering operation, dirty water from the pool comes in through the filter's inlet pipe, which leads to the water distribution head inside the tank. As pressure from the pump pushes the water down through the sand, the tiny sand particles catch any dirt and debris. At the bottom of the tank, the filtered water flows through the collector unit and out the outlet pipe.
Over time, the collected dirt and debris in the sand slows down the water flow. Pressure gauges are normally installed at the filter inlet and outlet to give an idea of the blockage level inside. If gauges show much greater pressure on the inlet pipe than the outlet pipe, this means that there is a build-up of dirt/debris in the sand. This means it's time to backwash the filter. To carry out a backwash, the water is redirected using the standard 6-way multiport valve supplied with all residential Filters or, in commercial applications, by adjusting the four or five-valve battery system (PVC ball or butterfly valves) which controls the water flow. To carry out the backwash, the return pipe leading to the pool is closed and the drainage pipe, which leads to a discharge area (such as a sewer system), is opened. By using the multiport valve or adjusting the valves in the system, the flow is redirected so that the water from the pump flows through what is normally the filter outlet. This reversal of the water flow means that water from the pump is pushed upwards through the sand, dislodging the dirt and debris. The dirty water then flows back through what is normally the filter inlet pipe and out through the backwash/drainage pipe.
In place of a sand filter, some pool systems use a diatomaceous earth filter or a cartridge filter. In a diatomaceous earth filter, water from the pool passes through filter grids coated with diatomaceous earth, a fine powder made from the chemically-inert, fossilized remains of sea organisms called diatoms. In a cartridge filter, dirty water passes through a filter made out of polyester cloth or corrugated paper. Instead of backwashing, you simply remove the filter and hose it off. Certain countries have laws that stipulate that entire volume of the water in the pool must pass through the filter in a certain amount of time – this can range from 30 minutes to eight hours and depends largely on weather conditions, frequency of use and bather load. Often, the pump and filter system is also connected to a well or municipal water line so fresh water can be added to the pool. This is necessary to replace water lost to evaporation, backwashing and "splash-out" (water that splashes on the deck or is carried out on people's bodies and swim suits).
Pool Filters
