The hydraulic oil is filtered off at a precisely defined pressure through a dried 0.8 µm membrane. The time and filtration volume are recorded. The test is ended after the filtration of 300 ml of oil, but at the latest after 2 hours.
The level I filterability value is calculated based on the actual filtration time for 240 ml of oil and the filtration time for the same volume of oil without membrane blockage.
The level II filterability value is calculated from the passage rates at the beginning and the end of the test.
The test is deemed "passed" for results over 50. The closer the result is to 100, the more easily filterable the oil. For results under 50, the oil is deemed "unfilterable".