The multipass filtration performance test which has recently gained industry-wide support offers many fundamental ways of describing the performance characteristics of fluid power filter elements. Some of these descriptions are uniquely qualified to provide the system designer with a practical technique for appraising the capability of filter elements. Important appraisal parameters of a filter element which must be considered by a designer are particle separation capability, contaminant capacity, and pressure loss.In order to specify a filter element properly for a given application, the requirements for the appraisal parameters must reflect the needs of the system components. A practical and fundamental description for the performance of fluid power filters will incorporate appraisal parameters which can be related to the demands of such system components.This paper relies upon the results of over 70 multipass filter performance tests to illustrate and substantiate the practical and fundamental descriptions presented herein. The filter elements represented by these test results cover a broad spectrum of the filters offered to the fluid power industry today. The interpretation of the test data presented is expressed in terms of basic performance descriptions, which can adequately serve the fluid power industry as appraisal parameters.