This document 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 according to 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 document allows the efficiency to be measured under both steady or cyclic flow conditions. It is also applicable to measuring the stabilized contamination levels that are produced by the filter element while testing with cyclic flow.

This document is not applicable to qualifying 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, e.g. the operating fluid or contamination.

The test data resulting from application of this document can be used to compare the performance of aerospace hydraulic filter elements.