To Build a Better Pump, First Develop a Better Filter

​If you’re sourcing a filter, KNF Flodos (Sursee, Switzerland), a maker of pumps used in medical and other applications, probably would not be on your short list of suppliers. You might want to rethink that, says Jean Delteil, Marketing Manager. In December 2012, the company introduced a pair of filters for a range of pumping applications. Why and how a developer of pumping systems branched out into filter fabrication is an object lesson in why necessity is still the mother of invention.

Noting that its laboratory dosing pumps required frequent maintenance, the company determined that particles, crystals and fibres, which are generally present in liquids and especially in acids, bases and solvents, were the root cause of the problem, and that an appropriate filtration system could eliminate it. A working group was formed to research available filters. It ended up testing 15 or so filters from all corners of the globe, none of which achieved the desired level of performance.

“We were looking for filters that met a specific set of criteria,” explains Delteil. “The filter body had to be available in three different materials—polypropylene, PVDF and Teflon—just like our pump heads. Also, the porosity of the filter layer had to be between 30 and 70 µm, and the filter needed to have the right —¼-28 UNF or the right hose barbs for tubes with a 4-mm inner diameter for Europe and 3.2-mm ID for the United States,” says Delteil. “None of the filters we tested even came close to meeting our needs.”

When a large Japanese pharmaceutical company that uses KNF’s lab dosing pumps requested an in-line filter, the decision was made to use in-house resources to develop effective filters. KNF Flodos analysed the chemical compatibility of the materials with more than 500 substances, and two materials stood out: PVDF and PEEK.

“PEEK, which is becoming increasingly popular in the medical industry, features chemical resistance similar to PTFE. Unlike PTFE, however, it can be injection moulded,” says Delteil. Using PEEK and PVDF allowed the company to meet more than 90% of the filtration requirements, he adds. On the manufacturing end, the company had to gain expertise in ultrasonic welding and working in an ultra-clean environment. Two filters are now on the market. The PVDF and PEEK filters, with a respective porosity of 70 and 35 µm, are available with male/female UNF connectors for tubes with inner diameters measuring 3.2 and 4 mm.

Developed for the company’s line of diaphragm liquid pumps, “the filters can be used in gear, micro-annular, syringe and piezoelectric pumps, and in devices that move liquids by means of gravity, suction or vacuum,” says Delteil. The products also are suited for filtering gases or air in medical or nonmedical devices, he adds, and in packaging machines used in the pharmaceutical and food sectors.

Norbert Sparrow