Cyclic Multi-Pass Tests of Hydraulic Filters using Taguchi Experimental Design Method to Identify Significant Test Parameters

Filter efficiency is one of many important performance indices that classify filters. Filter efficiency test methods, such as J1858 [1], MIL-F-8815D [2], and ISO4548-12 [3], etc., which vary from application to application and field to field, generally stem from ISO 4572 (4) and ISO16889 [5], the standard multi-pass test specifications. In most of the industrial/non-mobile applications, these methods serve their designed function perfectly. Also, most of these tests are based on the test parameters that can be controlled easily on a test stand and use other parameters related to particle counters and measurement technology available at the time of their release. However, in situations such as in rotary wing aircraft, fixed wing aircraft, and some mobile machinery where system vibration, cyclical flow, and cyclical thermal conditions are routine, filter efficiency obtained using standard test methods can be very different from that of the actual filter performance. Using the filter efficiency rating obtained from these standard test methods in the practice of filtration component selection can sometimes be misleading and provide poor correlation to the effectiveness of these components exhibited in field working conditions. In this paper, a filter efficiency test methodology using variable conditions and its associated test procedures are presented. Test results are obtained under vibration in two different directions, cascaded with variable flow amplitudes, pump response time, flow frequency, and thermal conditions. The Taguchi method is used in both experimental design and parametric analysis of filter element performance. A Pareto diagram is also presented as a general guideline for proper selection of key system factors that impact filter performance in such a way that shall lead us to obtain the realistic performance in terms of beta ratio/efficiency and life expectancy of a filter to suit its application.