The race is on in the pursuit of the highest grades of filtration for the pool and spa market — going beyond the “visible to the naked eye” and into the realm of small micron particles.
To that end, here’s how the cartridge has evolved from simple to sophisticated.
The cartridge, magnified
The most important aspect of filtration is the continual flow of water through the pump. A well-designed filter cartridge can optimize water flow, while catching the most dirt particles — big and small. As dirt is captured and starts building a “cake” on the cartridge, pressure in the filtration tank increases. This pressure affects certain efficiencies, such as power consumption and the service life of the cartridge.
The majority of filter cartridges use a nonwoven, spun-bonded polyester fabric. This nonwoven fabric, known as “tri-lobal,” comprises fibers that are sprayed onto a mobile belt in a random fashion to create the media. One of the fiber’s three “lobes” has a low-melt polymer, which randomly holds the media together. This is not a uniformly bonded fabric and, while performing moderately well, still had room for improvement.
The next leap forward was the “core and sheath” methodology, where all the fibers are evenly coated with a low-melt polymer, which bonds the fabric at each contact point. The result is a stronger fabric, which locks in the pore size distribution for capturing dirt of greater varied particle sizes, thus allowing the filter to clean the water faster and more efficiently.
Advances in development eventually led to the “point bonded” filtration fabric. This media contains more fibers per unit area to offer far greater volume and dirt holding capacity than other filtration fabrics. With reduced pore size distribution, the fabric provides superior turbidity reduction via unique localized cross flow filtration, which easily and efficiently captures dirt particles to achieve a deeper level of water cleanliness and clarity. With uniformly placed bonded weld spots and uniformly distributed fibers, the advanced-bonded fabric is strong and returns to a high state of original performance after cleaning. Further, it results in greater usability, longer cleaning cycles and less service time. A high-end manufacturing technology is used to create this new fabric, in which heat melts the fibers together. This technology also is presently used in the automotive and medical fields.
The core must be optimized for strength and filtration efficiency by allowing the maximum flow of water through the filtration media, while capturing the most dirt, yet remaining low in pressure drop. Different manufacturers use various techniques to build these inner cores — from polyvinyl chloride (PVC) pipe to injected molded cores comprising acrylonitrile butadiene styrene (ABS) or polypropylene (PP) thermoplastic used to allow varying rates of water to flow to the fabric’s surface area. Some filters also furnish an inner core support for extra strength.
Caps and bands
End caps provide structural support, increase filter cartridge durability, and need to withstand constant flow and pressure.
Filter cartridge pleats need to be sharp and precise to optimize flow and the ability to capture dirt; cartridge bands keep the pleats clearly defined to deliver performance.