Long Term Filtration of Hot Water

Who Filters Hot Water?

[ Mike Taylor, Delta Pure Filtration Mechanic, completes a successful leak test of a duplex filter assembly. The hot water filter system will be used in a food factory. ]

Because of our very economical stainless steel SH and SHJ series of stainless steel single-round housings, and our broad offering of filters, Delta Pure Filtration helps many customers with “hot water” filtration. It seems that a lot of people are in hot water. We help people with boiler water, equipment cooling water, hot water filtration for HVAC systems, hot tap water in hospitals, hot water in food plants, hot water for restaurants and coffee shops, and hot water to clean equipment. Some other applications for hot water that filter professionals will encounter are filters for hot WFI (water for injection) in pharmaceutical plants, and filters for hot steam condensate polishing in power plants. While each industry and each application will have its own unique requirements, some of the challenges associated with hot water are universal.

Misadventures in Hot Water Filtration

Water is one of the most aggressive solvents known to humankind – as such it is useful for dissolving ingredients, cleaning equipment and washing parts. Raising the temperature of water makes it even more aggressive.

It can be a big mistake to assume that a material is compatible with water, without actually checking. I made that mistake approximately 20 years ago when I recommended a filter with a glass medium (composed of glass fibers bonded by a resin) for filtration of hot water for a bottle washing unit. A day after the customer installed the filter, the filter was gone – completely disintegrated – potentially contaminating the insides of thousands of “cleaned” bottles. At first I was perplexed because the glass filter was marketed for, and successfully used in all manner of very- high-temperature applications, and the temperature of the “hot” water was well below the temperature rating of the filter. The lesson I relearned that day was that the published temperature limit of a material is contingent upon compatibility of the material with the filtered fluid – and that water is not automatically compatible with all filter materials. A problem for filter users and filter professionals alike is that hot water is not always listed in filter compatibility tables.

Glass is a popular Delta Pure Filtration material because it has a very high temperature limit and because it has a broad range of chemical compatibility. We advertise that our glass fiber filter medium in our DW Series filters can be used up to 399 deg C or 750 deg F (other filter components such as the core can limit temperature tolerance also.) Our customers use glass filters on various hot organic solvents and oils. We even have a new grade of glass that offers much improved acid resistance compared to some other grades of glass. But using glass for long term, continuous exposure to very hot water should be approached cautiously. Various internet sources suggest that water that is too hot will eventually etch and pit glassware in our dishwashers – and that our dishwasher water temperatures should be no more than 60 degrees C or 140 degrees F.i ,ii Nonetheless, I do see that some manufacturers advertise glass based filters specifically for hot water service – and those filters may be appropriate for certain hot water applications. Generally it is a good idea for the filter user to test a filter in any new application.

Certain plastic materials are subject to hydrolysis – a breakdown of the polymer in the presence of water or steam. Nylon and polyester are alluring materials because the temperature ratings of filters made from these materials tend to be “high”, but they are examples of polymers that will hydrolyze. The rate of hydrolysis of these polymers is “very slow” however, until one gets to hundreds of degrees C.iii One membrane filter company publishes a limit of 100 hours (about 4 days) of exposure of its nylon membrane filter with nylon hardware to 80 deg C water, but a similar filter with polyester hardware is not recommended at all for hot water exposure.iv The possibility for cumulative attack by hot (e.g., 80 deg C or 176 deg F) flowing water in long term use over several days or weeks has generally prevented me from recommending these materials for hot water in continuous service.

Filter Materials for Hot Water Filtration

So, generally speaking, what filter materials do I frequently recommend for hot water filtration?

SH and SHJ series single round filter housings are available in 304 and 316 stainless steel and are used for hot water applications up to 200F/97C.

For  the filter medium, I like polypropylene up to around 80 degrees C – note that polypropylene gets softer as its temperature is raised, even below the “melting” temperature. Up to water boiling temperatures I like polyphenylene sulfide (PPS) which is sometimes referred to by the tradename Ryton® (trademark of Chevron Phillips Chemical Company.) Yes, we do make PPS (or Ryton® ) string wound filters! An “up and coming” material for hot water pre-filtration is PVDF, sometimes known by the tradename Kynar (trademark of Arkema.) PVDF has been a popular material for submicron level membrane final-filtration of hot water for decades, and so has PES (polyethersulfone).

While polypropylene cores are generally ok to 80 degrees C, I often recommend metallic cores for even hotter water service, or in “very hot” applications where differential pressures could inadvertently get above 30 psid or so. At Delta Pure Filtration we consider the application and all the filter components – seals, hardware, etc. before making a recommendation.

When you don’t want to be in hot water but merely want to filter it, contact Delta Pure Filtration for assistance in selection of a filter assembly that will do the job.

*note: The comments in this blog were of a general nature. There are many types of water systems and each system and application will have its own unique requirements. We recommend that filters be selected and evaluated on a case-by case basis.

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i “Is Your Glassware Etched?” http://www.carterservices.com/is-your-glassware-etched/

ii “Water Quality Answers”, Water Quality Association, http://www.wqa.org/sitelogic.cfm?ID=351

iii DEECOM™: A NEW ECO-TECHNOLOGY FOR CLEANING METAL FILTERS, Longworth, et. al. http://www.bmlongworth.com/wp-content/uploads/2011/08/DEECOM1.pdf

iv “Ultipor® N66 Filter Cartridges For Microbial Reduction and Retention” Data Sheet FBN66WENa from Pall Corporation