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1.1 This test method covers determination of the wet filterability of lubricants and hydraulic fluids based upon mass flow rate measurements through a 0.8 µm membrane after ageing of the fluid in the presence of water. The procedure applies to lubricants and hydraulic fluids that are formulated with American Petroleum Institute (API) Group I, II, III, IV and certain V base stocks. Products formulated with water or base stocks that are heavier than water are out of scope.

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 Precision equipment and high pressure hydraulic machinery require filtered lubricants and fluids to prevent damage from the circulation of hard particulate contaminants. Three types of particulate contaminants are present in lubricants and hydraulic fluids: built in contaminants from the machinery assembly process, generated contaminants from equipment wear, and contaminants that enter from external sources. Water can also enter machinery lubrication and hydraulic systems through fill ports, defective seals, corroded heat exchangers, and reservoir breathers in the form of rain water, cleaning solutions, process water, metalworking fluids, coolants, and humid air.

5.2 The ability of lubricants and hydraulic fluids to retain their filterability in the presence of moisture is critical for efficient and reliable machine performance. Normally, the pressure differential across a filter will increase gradually as it accumulates dirt, sludge, and wear debris. In order to prevent the filter from collapsing, bypass valves in the filter assembly open when the differential pressure gets too high. If a filter becomes blocked by additives that precipitate due to the presence of contaminating water, the bypass valve will open. This can lead to a machine shutdown or circulation of damaging particles throughout the machine.