A swimming pool sand filter works through a process called mechanical filtration to keep the water clean and clear. It's a popular type of pool filter due to its durability, ease of maintenance, and efficiency in filtering small particles. Here's a step-by-step explanation of how it works:
Water Inflow: The process begins when water from the swimming pool is pumped into the filter tank. This water carries with it dirt, debris, and other particulates that are suspended in the pool water.
Filtering Through Sand Bed: Inside the filter tank, there is a bed of special-grade sand. As the water passes through this bed of sand, particles are trapped within the spaces between the sand grains. The sand essentially acts as a natural barrier or sieve, catching particles larger than a certain size (typically 20 to 40 microns).
Collection at the Bottom: After the water filters through the sand, it reaches the bottom of the filter. Here, a set of laterals (which are essentially a network of tubes with slots) collects the filtered water. The slots are small enough to allow water to pass but prevent the sand from entering these tubes.
Return to Pool: Once the water is collected at the bottom, it is then pumped back into the pool, significantly cleaner than when it entered the filter.
Backwashing: Over time, the sand bed becomes filled with trapped debris, which can reduce the efficiency of the filter and increase the pressure in the system, indicating it's time for cleaning. This is done through a process called backwashing, which involves reversing the flow of water through the filter. The water flowing in the opposite direction lifts the sand and the trapped debris, flushing it out of the filter through a waste line. After backwashing, the sand settles back down, and the filter is ready to resume its normal operation.
Rinsing (in some models): After backwashing, some filters require a rinse cycle. This involves running clean water through the filter for a short time in the normal direction of flow (but still being discharged to waste) to settle the sand bed and remove any remaining debris in the water before sending it back to the pool.
The efficiency of a sand filter can depend on several factors, including the size of the filter relative to the pool, the condition and type of sand used, and the regularity of maintenance activities like backwashing and sand replacement (typically every 5 to 7 years). This type of filter is particularly good for large particles and is favored for its simplicity and low maintenance, though it may not filter out fine particles as effectively as some other types of pool filters, like cartridge or diatomaceous earth (DE) filters.
