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How Does a Pool Sand Filter Work? - with Maintenance Tips

An image of a black pool sand filter.

Pool maintenance is crucial for ensuring clean and safe swimming conditions and a vital component of this upkeep is the pool filtration system, with sand filters being among the most common choices for pools in Australia. So let’s learn more about them. This article examines the workings of pool sand filters, how their individual components function, how they compare to other filter types, and provides maintenance tips that will help you keep your pool water crystal clear.

The Basics of Pool Sand Filters

The purpose of a pool sand filter is to maintain water clarity by capturing and removing debris and contaminants from the pool water. In simple terms, as water flows through the filter, particles such as dirt, leaves, and algae are trapped within the sand bed. This process effectively removes the impurities, leaving behind clean and clear water that is safe for swimming.

The structure of pool sand filters is not overly complex. They consist of several components, namely: 

  • Filter Tank: The main housing unit where the filtration process occurs.
  • Sand: The filter medium that traps impurities from the water as it passes through.
  • Multiport Valve: Controls the flow of water through various filtration modes (e.g., whether you wish the water to be filtered and sent back to the pool or let it go to sewage).
  • Pipe with Laterals: The laterals take in the filtered water but block the sand particles and send it back to the pool through the plumbing.

Filtration Process

The filtration process begins when the pool pump draws water into the filter tank, initiating the journey towards clean water. The water is always brought to the top of the tank (either because it enters from the top or because it enters via a pipe on the side and is pumped to the top) as the filtration process requires it to trickle from top to bottom.

The water is spread out evenly over the sand bed by a distributor - a small device that functions like a mini-fountain. The sand is meticulously arranged to create an effective filtration barrier. As the water encounters the bed of fine sand and slowly drains towards the bottom, the turbulence of the water flow causes suspended particles, ranging from dirt and debris to organic matter and even microscopic algae, to collide with the sand grains. It is important to note that more and more glass is being used in place of sand in media filters as it works in much the same way.

The sharp edges and irregular surfaces of the sand or glass media act as natural traps, capturing these contaminants and preventing them from circulating back into the pool. Larger particles are swiftly ensnared, while smaller impurities are also intercepted through repeated cycles of filtration. The water that reaches the bottom of the tank is cleaned and purified, typically ready to be sent back to the pool (or ready to be sent to waste, if you are doing backwashing, but more on that below). 

The water at the bottom of the tank enters the pipe through the laterals; the openings on the laterals are small enough that they take in the water but block sand particles from entering the system. The filtered water is then sent back to the pool. This continuous process of filtration not only maintains the aesthetic appeal of the pool but also upholds the essential standards of hygiene and safety for swimmers.

However, over time, the sand bed becomes clogged with trapped debris, reducing the filtration efficiency. To clean the sand, the filter's multiport valve is set to backwashing (on most pool sand filters this position is called ‘waste’), reversing the flow of water through the filter. In this process, the water enters the sand bed through the laterals, picks up particles from the sand until it reaches the distributor and is then sent to sewage.

After the backwashing process is completed, the system should be rinsed, and then the clean sand can continue filtering the pool water by setting the valve back to filter - these are the basics of sand pool filter cleaning. Backwashing doesn’t take long and can be done within a few minutes, depending on the model of the filter.

Pros and Cons of Sand Filters

A pool sand filter is just one type of filter that exists, which also means it has its advantages and disadvantages when compared to the other types.

The pros of sand filters are:

  • Effective at trapping large particles, such as leaves and debris, contributing to visibly cleaner water.
  • Requires relatively little attention and servicing.
  • Cost-effective initial investment for pool owners, offering a balance between affordability and performance.
  • Compatible with most pool systems and setups, making them a versatile option for various pool types and sizes.

The cons are:

  • Less effective at capturing small particles and microscopic impurities, which may require additional filtration methods for optimal water quality.
  • Requires regular backwashing and occasional sand replacement, adding to maintenance efforts and costs over time. If space or sewer access are an issue then a cartridge filter is a better option.
  • Backwashing lowers the pool water and thus can lead to a chemical imbalance as new water is brought into the pool.

How Long Does a Sand Filter Last?

An image of a Sensa Clear media filter.

The lifespan of your sand filter will depend on several factors, including the quality of the sand used, how frequently you maintain it, and your pool’s water chemistry. In general, with proper care and maintenance, a sand filter can easily last anywhere from 5 to 7 years and even up to 10 years without needing replacement.

This longevity is another advantage of sand filters because if we were to compare sand filters vs. cartridge filters (the other common type of pool filter), the sand filter would be far more durable; the typical lifespan of cartridge filters is around 5 years while the filter element should be replaced once a year.

What Pool Types Are Sand Filters Best For?

The final advantage of sand filters is that they are perfectly suitable for all types of pools - that includes both inground and above-ground pools. The only thing you need to be conscious of is that the filter matches the pool size, as that is the only thing that will affect the sand filter's efficiency.

Pool Sand Filter Maintenance Tips

Finally, to ensure optimal performance and longevity of your pool sand filter, follow these simple maintenance tips:

  • Regular Backwashing: As we explained above, backwash the filter as needed to remove trapped debris and maintain proper flow.
  • Sand Replacement: Replace the sand every 5 to 7 years or as indicated by decreased filtration efficiency.
  • Inspecting and Cleaning Components: Regularly check and clean the multiport valve, filter tank, and laterals to prevent clogs and leaks.
  • Water Testing and Chemical Balance: Maintain proper water chemistry to prevent algae growth and optimise filter performance.
  • Seasonal Maintenance: Winterize the filter for off-season storage and ensure proper startup in the spring.
  • Professional Servicing: Seek professional help for complex maintenance tasks or repairs beyond your expertise if you feel the need.

Shop Pool Filters Online

Understanding how a pool sand filter works and implementing proper maintenance practices are essential for keeping your pool water clean and inviting and prolonging the filter’s lifespan. However, at some point, you may need to replace the sand filter or even wish to change the type. 

If that is the case, you can buy pool sand filters and cartridge filters at Direct Pool Supplies. Our range only includes filters from trusted brands like Aquatight, Davey, Zodiac, and more. Simply place your order online and we will ship it to your address. Feel free to contact us if you have any questions about filters or other pool equipment or wish to learn about our policies. 

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