Ability of a filter to retain specific test contamination in a hydraulic fluid with a specified contamination concentration under defined test conditions (CETOP RP 100).
As the test method for filtration efficiency in general the multipass test according to ISO 4572 has become established. However, the results obtained with this test cannot be simply transferred to practice, as in relation to the conditions during the test there is a series of system effects, such as filter size, the velocity of the flow rate, pressure and differential pressure conditions among others.
As a measure for the filtration efficiency in general either the filter efficiency or better the β value is used.