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The purpose of filtration is to make sure that the hydraulic fluid conforms to the purity class required for the components in question.
It is not a case of filtering particles from a certain size onwards out of the fluid, but of making sure that this constructively defined purity class (generally based on NAS or ISO ratings) is maintained for the entire lifetime of the hydraulic system.
The individual steps and main parameters involved in selecting a filter system are as follows:- Determination of the required oil purity class for the hydraulic system according to ISO 4406 / NAS 1638
- Ascertainment of the environment and range of application, as well as of the oil quality
- Selection of filter
Suction filter integrated in or mounted on tank, suction/return filter, line filter, return filter, aeration/deaeration filter.
Special attention must be paid to hydraulic parameters such as filter size in relation to nominal volumetric flow, mounting dimensions and possible restrictions or fixing dimensions.
Max. admissible pressure drop via filter.
Contamination indicator, bypass valve.
- Selection of filter element
Assessment of filter output based on the rule beta-value ³ 75 according to ISO 16889.
Filtering area, specific dirt holding capacity (e.g. measured in mg/100 cm² according to ISO MTD test dust, specific filtering surface load.
Filter lifetime, Dp-Q characteristics.
Element stability, fatigue strength, bursting pressure strength, influence of pressure pulsations on efficiency of filter element, compatibility factors.
- Assessment of maintenance interval based on parameters such as operating conditions and specific pollutant status SPS.
All of these points must be defined in relation to the system as a whole in order to guarantee the required purity class. Once the filter has been selected by the design department, the separation capacity in terms of specific particle sizes, retention rate, dirt holding capacity and service life are the determining factors which need to be considered with regard to quality and economy of filtration.
There are even more factors to take into account, however, which come under the heading of „overall optimisation". To take the example of return filter: is it not sensible to consider the entire tank/filter system rather than just the filter? As for bypass filtration, it is essential to deal with the finest impurities in order to guarantee long-term maintenance of the purity class. With the combined element, we will gladly demonstrate how bypass filtration can be integrated into the standard filter housing without a separate bypass circuit.
Your job is to design and produce optimal solutions for your customers. Ours is to assist you in this task by guaranteeing optimal filtration for the entire lifetime of the system at minimal cost.
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