Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/1412702
10 | September - October 2021 | www . machinerylubrication.com this uncertainty and random interpretations of such performance claims. Figure 6 shows data from a sample multipass test report to ISO 16889. Fabrication Integrity Testing You may be surprised to hear that each filter that is sold is a filter that has never been tested. Multipass filter testing is destructive, time-con- suming and relatively expensive. It is also really good at assessing the first three performance assessments in the above list. While many filter companies may share or publish multipass filter test data with customers, often these tests were last performed years ago. Filter media changes, as do other manufacturing specifications. ese differences influence test performance in a variety of ways. Fabrication integrity testing (also known as bubble-point testing) presents another option and is often done on each filter before multipass testing. Fabrication integrity testing is non-de- structive and relatively cheap, although it is rarely done on filters that are sold. To perform this test, the filter element is submerged in a bath of alcohol, and air is slowly metered into the center of the filter. e increasing air pres- sure is monitored using a standard monometer. When the first stream of air bubbles emerges through the filter element (point of least resis- tance), the pressure reading of the monometer is noted. is is the bubble point. e higher the pressure, the greater the filter's fabrication integrity. ere is a good correlation between the bubble point and the mean pore size of the filter media. Most filters that fail the bubble point test are not margin- ally defective but instead exhibit major issues, including damaged filter media, seam cracks and defective end-cap adhesive seals. You may be surprised to learn that at least 10% of all new oil filters (regardless of the application) will fail the bubble point test in this way. is statistic can vary between filter brands, type and quality (e.g., price point). Using Testing to Reduce Your Filtration Spend e value of incorporating filter testing when planning your purchases is best demon- strated using a simple financial analysis. Let's say your company spends $152,000/year on a single type of hydraulic filter. You are aware that there are at least three filter suppliers that make comparable filters (size, configuration and performance). e prices of these filters are different. In the past, the low-cost option was selected by procurement. For the purpose of this analysis, we'll assume the capture effi- ciency (Beta Ratio) of these three filters to be the same. Which one should you select? e lowest price? Let's do the math. See Figure 8. Getting a filter's dirt-holding capacity is rarely as simple as going to a website or looking at a product data sheet. In fact, I'll COVER STORY Brand A Brand B Brand C Filter cost (per element) $125 $110 $95 Tested dirt-holding capacity (ISO 16889) 250 gms 160 gms 125 gms No. of filters required to remove 200 kgs of dirt (fleetwide) per year (filters changed based on pressure drop) 800 1250 1600 Annual filter consumption cost $100,000 $137,500 $152,000 Filter change labor cost (est. $25 each) $20,000 $31,250 $40,000 Total annual cost (filter and labor) $120,000 $168,750 $192,000 Savings compared to the economy Brand C $72,000 $23,250 $0 Figure 7. The test bench on the left is used for bubble point testing (ISO 2942). The im- age to the right shows a stream of bubbles from a defective opening in the filter media. The air pressure reading when the first bubble appears is recorded as the bubble point. Figure 8. Financial analysis of three filters based on dirt-holding capacity. Data from filter testing guides the decision. In this case a premium, long-life filter is the economi- cal best choice, saving $72,000/year.