This part of ISO 14085 specifies a method for determining the resistance of a filter element to flow fatigue caused by varying flow through the filter in various stages of the filter contaminant loading process. The filter is subjected to a uniform varying flow rate for a specified number of cycles, at a number of predetermined differential pressures. Although the number of cycles and differential pressure conditions used in this part of ISO 14085 is meant to simulate possible service conditions, this part of ISO 14085 is not intended to qualify a filter element under replicate conditions of service; this can only be done by a specific test protocol developed for the purpose, including actual conditions of use, for example the operating fluid, contamination, and exact cyclic flow conditions. This part of ISO 14085 establishes a method for verifying the ability of a filter element to withstand the stress caused by cyclic differential pressures induced by a variable flow rate. The test data resulting from application of this part of ISO 14085 can be used to compare the performance of aerospace hydraulic filter elements.