This part of ISO 14085 describes two methods to measure in repeatable conditions the filtration efficiency of filter elements used in aviation and aerospace hydraulic fluid systems. It can be applied when evaluating the overall characteristics of a filter element per ISO 14085-1, or separately.

Since the filtration efficiency of a filter element can change during its service life as it is clogging, this test method specifies its continuous measurement by using on-line particle counters with continuous injection of test contaminant and recirculation of particles not retained by the test filter element until the differential pressure across the element reaches a given final or “terminal” value.

This part of ISO 14085 allows the efficiency to be measured under both steady or cyclic flow conditions. It also is applied to measure the stabilized contamination levels that are produced by the filter element while testing with cyclic flow.

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 or contamination.

The tests data resulting from application of this part of ISO 14085 can be used to compare the performance of aerospace hydraulic filter elements.