We occasionally get asked about swimming pool sand filters from people who have never owned a swimming pool before. Apart from the lessor used diatomáceos earth (D.E.) filters there are two basic choices for pool filtration systems which are sand filters and cartridge filters.

In Spain and Portugal it is far more common to find a sand filter system for domestic swimming pools. They work through a process called mechanical filtration. The video, by an Indianapolis based company, explains how a sand filter system works. Although the video is from the USA, the filter system is the same as most of those you find in Spain or Portugal.

If you prefer to read about this topic we also explain below how pool sand filters they work:

Filter Tank: The filter system consists of a large, cylindrical tank made of fiberglass, metal, or other durable materials. Inside the tank, there is a bed of specially graded pool filter sand.

Inlet: Water from the pool is pumped into the filter system through an inlet pipe. This water is typically a mixture of clean water and water laden with dirt, debris, and contaminants.

Distribution System: The incoming water is distributed evenly over the top of the sand bed by a diffuser or distribution system. This even distribution helps ensure that the water is properly filtered as it passes through the sand.

Filtration: As the water flows down through the sand bed, the sand particles trap and remove impurities and debris from the water. This process of physical filtration relies on the size and shape of the sand particles to capture particles as small as 20 to 40 microns in size. Larger particles are trapped on the surface of the sand bed, while smaller particles may penetrate deeper into the sand.

Clean Water Collection: The clean water that passes through the sand bed is collected at the bottom of the filter tank. It is then directed through an outlet pipe, which carries the filtered water back to the pool.

Backwashing: Over time, as the sand becomes clogged with debris and impurities, it becomes less effective at filtering the water. To clean the filter and maintain its efficiency, a backwashing process is performed. During backwashing, the flow of water is reversed, and water is pumped up through the sand bed, dislodging and flushing out the trapped debris. This dirty water is then discharged to waste, away from the pool.

Rinse Cycle: After backwashing, a short rinse cycle is typically performed to settle the sand bed and ensure that any residual debris is removed before returning the filter to its normal filtration mode.

Continuous Operation: The filter system continuously circulates water from the pool through the filter and back into the pool, maintaining water clarity and cleanliness.

Periodic Sand Replacement: Over time, the sand in the filter becomes worn and less effective at filtration. Depending on usage, it may need to be replaced every 5-7 years.

In summary, pool sand filters work by mechanically trapping and removing impurities and debris from pool water as it passes through a bed of specially graded sand. Regular maintenance, including backwashing and occasional sand replacement, is essential to ensure the filter continues to operate efficiently and keeps the pool water clean and clear.