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Many filter cartridges look the same. Does that mean they work the same?
When it comes to pleated filter cartridges, the elements can sometimes look the same. Unicel differs from their competition in that they have always used Reemay brand, 100% polyester fabric in their cartridges. In fact, in the mid-1960s, we engineered Reemay in partnership with DuPont to replace the paper-based materials that did not hold up in the swimming pool environment. Moreover, Reemay was engineered to balance durability, cleanability and efficiency of the filter and optimize its performance.
For non-Reemay alternatives, it is important to know how the fabric is finished in the production process – specifically, how all the fibers are bonded together. One of the alternatives on the market right now is point bonded, also referred to as needle finished. The fundamental problem with this type of finish is that at each of the bond points the material is fused closed and water cannot flow through it. This can reduce the initial filtration area by up to 25%. Imagine a quad filter system with only 3 elements worth of filtration area in it. That’s essentially what you have if the cartridges are made with a point bonded fabric.
Filter manufacturers that use point-bonded material tout how quickly the cartridges load and clean up the water compared to elements made from Reemay. What they fail to mention is the tradeoff between this efficiency and how often you need to clean the filter and how easy it is to clean. Cartridges manufactured with point bonded material will have shorter cycle times than cartridges manufactured with Reemay, meaning they will need to be cleaned more often. Also, the point bonded surface is more difficult to clean than the flat bonded, smooth surface of the Reemay elements. It is important to recognize this tradeoff between efficiency and cleanability.
Cartridges that look the same may also have different fabric basis weights. You should ensure that the filter you are buying has the basis weight as the OEM originally specified. Basis weight is the ounces of fiber per square yard – for our industry today this is largely 3 oz. and 4 oz. If the OEM specified a 4 oz material for their system, for best performance don’t accept a 3-ounce alternative.
Excerpt from “Understanding energy-efficient filtration: How filter sizing and selection influences hydraulic efficiency – it’s trickier than you might think” (Aqua October 2018, p 91-92.)
A Systems Approach
With so many factors influencing a filter’s hydraulic performance, its best considered in context of a breadth of factors such as the plumbing size and layout, the hydraulic characteristics of other component, the desired turnover rate, and environmental factors.
“When we talk about efficiency and filtration,” says Christine Schaeffer, President of Unicel, “it’s almost always about water efficiency. For example, how much water does it take to clean a sand, D.E. or cartridge filter? I’m not at all sure people are giving much thought to how much less or more energy efficiency is based on the filter element.”
Schaeffer does acknowledge that improving hydraulic efficiency of the system as a whole is an important objective, and she is enthusiastic about the role cartridge filters can play in that effort, especially with the use of variable speed pumps. But she also stresses the importance of taking a systems-based approach.
“When you consider the marginal contribution of the filter element, the punchline requires ‘all things be equal,’” she says. “But in our industry you can’t hold all things constant. Consider, for example, how each subsequent pass of water through the filter changes the equation. You can’t even hold the important variable constant for two passes. Conceptually it makes sense that the filter element plays a part, how I am not clear that you can measure the difference made by the filter elements.
She concludes: “When we take into account the many variables in the filter system itself, the environment and the way people maintain the pool, the bather load and the characteristics of the bathers, we have a systems approach to filter element performance and can better speak to the relationship between the filer element and hydraulic efficiency, although we may not be able to strictly qualify it.