Pool cartridge filters work by trapping debris and contaminants as water flows through pleated polyester or paper media. The pleated design increases surface area for better filtration, capturing particles as small as 10-15 microns through physical straining.
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Pool cartridge filters work through physical filtration, using pleated polyester or paper media to trap debris and contaminants as water passes through. The pump pulls water from your pool, forces it through the cartridge's microscopic pores, and returns clean water to the pool. This simple yet effective system can capture particles as small as 10-15 microns.
Understanding how your cartridge filter operates helps you maintain it properly and recognize when it needs attention. The process begins when your pool pump creates suction that draws water from the main drain and skimmer lines.
Water enters the filter housing through the inlet pipe and flows around the outside of the cartridge. The pump's pressure forces water through the pleated filter media from outside to inside. Clean water then exits through the center core of the cartridge and returns to your pool through the return jets.
This outside-to-inside flow pattern is crucial because it allows the outer surface of the cartridge to capture larger debris first, while finer particles get trapped in the deeper layers of the media. This design maximizes the filter's dirt-holding capacity and extends its cleaning cycle.
The heart of any cartridge filter is its pleated media, typically made from spun polyester fibers or specialized paper. Most pool cartridge filters are rated between 10-15 microns, meaning they can capture particles larger than this size. To put this in perspective, human hair is about 70 microns thick, so these filters catch debris much finer than what you can see.
The pleated construction serves multiple purposes. First, it dramatically increases the surface area available for filtration - a typical pool cartridge has 40-60 square feet of media in a compact cylinder. Second, the pleats create depth filtration, where particles get trapped at various levels within the media rather than just on the surface.
Your filter system operates within specific pressure ranges, typically starting at 8-12 PSI when the cartridge is clean. As debris accumulates, pressure increases because the pump must work harder to force water through the clogged media. Most systems require cleaning when pressure rises 8-10 PSI above the clean starting pressure.
Cartridge filters work best when water flows through them at appropriate speeds. Too fast, and particles don't have enough contact time to get trapped. Too slow, and you're not getting adequate turnover. Most residential cartridge filters are designed for flow rates between 15-30 gallons per minute per square foot of media area.
Several factors affect how well your cartridge filter performs. Water temperature plays a role - warmer water is less dense and flows more easily, potentially reducing contact time. Pool chemistry also matters, as proper pH levels (7.4-7.6) help particles clump together, making them easier to filter out.
Cartridge filters excel at removing organic debris like leaves, insects, and algae, as well as inorganic particles like dust and sand. However, they're less effective against very fine particles or dissolved contaminants. For these, you'll need proper water chemistry including adequate free chlorine levels based on your CYA (stabilizer) level.
Regular cleaning is essential for optimal performance. The standard cleaning process involves removing the cartridge and rinsing it with a garden hose to remove loose debris. For deeper cleaning, soak cartridges in a filter cleaner solution every 3-4 cleanings to remove oils, lotions, and embedded particles that water alone cannot remove.
Many pool professionals recommend keeping two sets of cartridges - one in use while the other dries completely after cleaning. This rotation system extends cartridge life because fully dried media regains some of its original porosity. Wet cartridges tend to load up with debris faster than completely dry ones.
Even with proper cleaning, cartridge filters eventually wear out. Signs include cartridges that won't come clean despite thorough washing, frayed or damaged pleats, or inability to maintain normal operating pressure. Most quality cartridges last 12-18 months with proper care, though heavy use or poor water chemistry can shorten this lifespan.
While cartridge filters are excellent for routine filtration, they have limitations. They cannot remove dissolved metals, extremely fine particles smaller than 10 microns, or kill bacteria and algae - that's your sanitizer's job. Understanding these limitations helps you maintain realistic expectations and recognize when additional treatment methods are needed.
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