Sand Filters Designed To Remove Debris From A Swimming Pool.
The tank is filled with a special grade of filter sand to about 2/3 of it's depth. There is a system of fine collectors called laterals installed in the bottom olf the tanks. These are moulded with slots small enough for water to pass, but not the grains of sand. The water is forced into the filter tank by the circulation pump, normally via a multiport valve.
The multiport valve is an integral part of the filter system, as it directs the water around the tank, changing it's direction of flow for different operations.
In the filtration cycle the water is directed into the top of the filter tank, and evenly diffused via a spreader or rose. The water then passes down through the sand bed. The largest debris is trapped on the surface. Smaller particles pass down into the sand bed, but are normally trapped within about 2".
The filter can be run in this mode for about a week at a time. Then a backwash is carried out. In this the water flow is directed into the bottom of the filter and up through the sand bed. The flow needs to be fast enough to "fluidise" the sand bed, and this then lifts out all the dirt.
The multiport valve directs the water out through the waste port, and so into a drain. The filter is then run for 10-15 seconds in a rinse cycle, which compacts the sand bed, and the water still runs to waste. The valve can then be set back to the filter position and the sytem left running.
The size of filter required for your pool is calculated on the flow rate required to filter your pool volume in a certain time. This then needs to be matched up to a suitable pump, and the correct number and size of pipes and fittings to flow the water to and around the pool basin.
The filter sand should be replaced about every 4-5 seasons for an outdoor pool. |
