ISO HYDRAULIC FLUID POWER – FILTERS – MULTI-PASS METHOD FOR EVALUATINGFILTRATION PERFORMANCE OF A FILTER ELEMENT. Introduction. The obsolescence of AC Fine test dust (ACFTD) has led to the adoption of a new test dust, ISO Medium Test. Dust (ISO MTD), and the impending. ISO Multi-Pass Test. The multi-pass test is a means of determining a filter’s performance; it measures the ability of the filter to remove particles of test dust.
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While primarily developed for fluid power, 16898 new standards are equally applicable to the lubricating oil sector. These standards have been developed to increase the precision in the measurement of contamination and filtration performance, and to extend the amount of information from the tests.
Additionally, the user can have greater assurance and confidence 116889 the data, and designers or specialists can make a more informed judgment in the selection of the most appropriate filter for his system.
This article will focus on the impact the new standards have on selecting candidate filters based on performance criteria.
To appreciate the importance of the filter in the management of the system, consider the primary function of the filter: It has to protect the components from the damaging, critical clearance-sized particles particles that can penetrate and interfere with the working clearances of components.
The filter should control the fluid cleanliness to a level that is equal to the performance, life and reliability of the system required by the user. It should allow fluid to pass through at the given flow with the minimum pressure drop DP to minimize stress and energy losses.
Hydrauliköl-Filtrationssysteme | Donaldson Hydraulik
A filter must control the levels of all contaminant particles at and above the size critical to its operating system. If the filter fails to provide the necessary control of damaging-sized particles, then their presence in the system will lead to a substantial increase in the 1689 of particles generated within the system through a chain reaction of wear.
Particles entering component working clearances will become work hardened and produce more wear particles. This makes the capture of these particles, by the filter, essential to sustain the good health of the system.
This gives a series of Beta ratios for the filter 116889 opposed to a percentage efficiency.
The Beta ratio is defined as:. The need to remove particles consistently across a wide size range was recognized by the ISO Working Group responsible jso updating the multi-pass filter test.
The group also stipulated that detailing comprehensive performance data was necessary so users can make informed selections. The data that can be made available is as follows:. The current data requirement is a substantial improvement. Most manufacturers published ratings at other sizes but there was no consistency. Users were often confused when comparing performance data of seemingly identical filters. Now, users can quickly see how the filter performs over a specified range of particle sizes and can compare the 1689 of candidate elements.
The slope of the curve effectively defines the pore size distribution PSD of the filtration medium; the wider the PSD the less able the filter is to control those critically sized damaging particles. When the contaminated hydraulic fluid passes through the filtration medium, it takes the line of least resistance.
This will be through the larger pores in the medium and any holes created by poor manufacturing techniques.
Therefore, the desired level of control will not be achieved. It is able to control the critically sized particles better than Element B.
Clarifying the New ISO Contamination Filtration Standards
Users of filters have historically liked the simplicity of a single point rating the size where a specified Beta ratio is attained. Consequently, the number of different Beta ratings used has proliferated. What value is most appropriate? Therefore, the highest Beta isl that can be reliably measured should be selected. However because of particle count statistics in the multi-pass test, the absolute rating cannot be measured with any degree of confidence.
In the s and s, a compromise was reached between what is desirable and what can be consistently achieved for the range of filters assessed by this test. This is essential to achieve the required system reliability and life.
It also enables the user to discriminate between elements that achieve the desired control and those that do not. Figure 2 shows the advantages of this approach. It is only when the ratings at higher Beta ratings are considered that the differences in performance are clearly seen.
The effectiveness of the hydraulic filter to control clearance-sized particles is essential if the desired level of ios is to be realized in the hydraulic system concerned. This demands care in 1889 selection of the most appropriate filter for the system. The changes in the ISO multi-pass test method and associated 1889 provide greater precision in measurement. More detailed information from the test has to be published than previously required.
However, the multi-pass test is carried out in a laboratory under steady-state conditions and does not represent strenuous operational conditions. It is a preselection requirement that provides the user and specifier of filter standards with more consistent information.
The more critical the system, the stronger the filter element and the more frequent the monitoring required. Toggle navigation Toggle search. Current Issue Archive Advertise. The Role of the Filter To appreciate the importance of the filter in 116889 management of the system, consider the primary function of the filter: The Beta ratio is defined as: The data that can 168889 made available is as follows: About the Author Mike Day.
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