The Oil cleanliness level should be selected with the most critical component, you are trying to protect. E.G., a servo valve requires cleaner oil (ISO CODE 16/14/11), then a gear pump or motor (ISO CODE 19/17/14).

Most machine and hydraulic component manufacturers specify a target ISO cleanliness level to equipment in order to achieve optimal performance standards. It is always best to consult with components manufacturers and obtain their written fluid cleanliness level recommendations. It may also prove useful for any subsequent warranty claims.

The ISO 4406:1999 (International Standards Organization) cleanliness level standard. It is based on three range numbers representing 4/6/14 micrometers particle counts per milliliter of sample fluid. The two sizes were selected due to the fact that smaller size was thought to be representative of the fine silt present in the fluid, and the larger size was indicative of the wear contaminants present.

Particulate contamination is generally classified as silt or chips. Fine particles or silt, can be defined as the accumulation of particles less than 6 micrometers over time. This type of contamination causes system component failure over time.

Overfiltering relates to the use of a finer filter, when a course filter will do. E.g. In trying to achieve a cleanliness level of 16/14/11. A filter with an efficiency of Beta6=200, will accomplish this . However, a filter with an efficiency of Beta3= 200 will also achieve this cleanliness level and more but at what cost?

The multipass test is used to determine the efficiency of the filter media. This method simulates a real world system by continually adding a known contaminant to the fluid as the filter removes it. They continue the test until the filter medium becomes so loaded with contamination that the pressure drop across the element becomes excessive. Samples are simultaneously taken upstream and downstream of the filter several times during the test to get time average efficiency ratings over the useful life of the element. These samples are counted on a particle counter to give accurate results. The upstream counts are divided by the downstream counts. This forms a simple ration, where x equals the particle size.

The weight of a specified artificial contaminant which must be added to the influent to produce a given differential pressure across a filter at specified conditions. Used as an indication of relative service life.

A filter element which when loaded contaminant can be restored by a suitable process (usually ultrasonic cleaning) to an acceptable percentage of its original dirt holding capacity.

A coalescing type filter is designed to remove oil and water aerosols by means of coalescence. (e.g. by intercepting and concentrating aerosols into larger droplets that can be collected and removed from the filter).

The differential gas pressure at which the first steady stream of gas bubbles is emitted from a wetted filter element under specified test conditions. Bubble point test are conducted by immersing the filter element in a liquid. A measured air pressure is applied to the outlet of the element in such a manner that it is applied to the porous wall of the element from the inside to the outside. While the element is held horizontally, beneath the surface of the test liquid and is rotated, the air pressure is slowly increased until a steady stream of air bubbles appears on the outside of the filter medium and breaks away toward the liquid surface. The air pressure requires to blow the first stream through a pore is inversely proportional to the size of the largest pore in that element. The bubble point test is an excellent means to determine the integrity of the element.