The Water Quality Assn. (WQA), a founding member of the European Drinking Water (EDW...
Key factors to consider when matching the housing to the cartridge and application
Whether a filter system is installed in a residential, commercial or industrial application, the cartridge often is thought of as the heart of the system because its chemical and physical properties determine the filter’s effectiveness in removing specific materials suspended in fluids. Flow rates, the fluid’s contact time with the filtering medium and pressure drops, as well as environmental characteristics such as exposure to extreme temperatures, pressures and corrosive materials will affect the choice of a cartridge.
However, the cartridge operates within a housing, and even a cartridge that is perfectly matched to the application won’t perform adequately if it’s not also matched to a housing that meets the same application requirements. Specifying them together as an integrated system is the best way to assure they provide optimal performance.
There are many sizes and styles of housings that are made from a variety of materials and come equipped with features to enhance performance in a range of applications. Selecting the most appropriate housing involves both science and art, but it’s a relatively simple process of matching the housing to the cartridge and the application requirements using the following key factors:
Because it’s almost impossible to find a filter housing that optimally addresses each factor, the ultimate choice may be the result of making compromises. In the case of large-scale applications featuring many housings, it is often advisable to test the filter on a more limited scale to make sure it performs to expectations before rolling it out across the installation.
Low Flow Rates
Flow rates can be critical in determining the inlet and outlet size of the housing, as well as the number of housings that may need to be connected in parallel to achieve the desired pressure drop. Lower flow rates are achieved with larger cartridges or more housings. The savings in cartridge change out labor and better utilization of the filter cartridges can be significant. This is especially important in industrial or food service applications where down time is costly.
Fluid Temperature & Operating Pressure
Housings are made of various materials to maximize performance in different applications and environments. The temperature of the fluid being filtered is important in determining whether or not the material from which a housing is constructed is appropriate for a given application. Talc-filled polypropylene housings can be used with temperatures up to 125°F in general water filtration. Temperatures up to 160°F can be handled by glass reinforced nylon housings. Temperatures up to 300°F typically are handled by stainless steel housings.
Peak operating pressures also determine the materials of which a housing should be made and, therefore, its cost. Talc-filled polypropylene works with pressures from 90 to 125 psi depending on the size of the housing. Some stainless steel housings can operate at pressures up to 250 psi. For higher pressures and temperatures, specialty housings will be required.
Chemical compatibility will be a factor primarily in the commercial and industrial markets where different liquids, strong bases or acids may be encountered. Care must be taken to specify housings that maintain their performance characteristics in these environments. Installing housings that will be exposed to chemicals to which they are incompatible may cause damage and result in failure.
Most manufacturers have chemical compatibility tables for quick reference with commonly encountered chemicals. If the user cannot find the answer or wants a second opinion, he or she should not hesitate to call the manufacturer for technical support.
Meeting Performance Expectations
Independent certification of the manufacturer’s claims is one of the most important value-added features. Having an independent third party use scientific testing to verify the manufacturer’s claims may provide some peace of mind in an ever increasing litigious business environment. Housings may be tested and certified through NSF. Make sure that components have received an NSF Standard 42 component listing—the minimum listing required for drinking water applications. This certifies the materials will not leach harmful contaminants into the water and that the housing passes the minimum structural requirements of 100,000 cycles of 0 to 150 psi and minimum burst of 500 psi or four times recommended operating pressure.
To be confident that the product bought off the shelf performs to the levels of those tested, purchase a housing from a company that is ISO9000 rated. This rating certifies that the manufacturer has met strict quality criteria for standards in the manufacturing and design process.
It is important that the cartridges and housing used are made from the same manufacturer. While cartridges and housings may look alike, there are important differences. Each manufacturer designs its cartridges to fit the exact dimensions of its housings. Mixing cartridges and housings can lead to a bypass of the cartridges’ seals resulting in poor performance, which could be a liability burden if health claims are made. This is the reason that NSF tests cartridges and housings together and discourages the use of cartridges built by one manufacturer in the housings built by another. wqp