Matthias Jung /Product Manager for Filter Elements / Argo Hytos GmbH /www.argo-hytos.com
Recent detailed analysis of fluid flow through a range of filter materials has led to a better understanding of conditions inside a working hydraulic-fluid filter. The work has let our company identify the key factors responsible for pressure loss in the folded material.
The result is a special web technology for production of a new hybrid fabric that maintains an optimal opening of the fold channels. Thus pressure loss in the folds drops as much as 50%.
What we learned
To improve performance of a filter, as well as increase its dirt holding capacity, it is necessary to reduce its pressure loss. Calculations show that specific flow resistance depends on the filter materials, as well as on the structure and length of the intermediate fold gaps, the so-called fold channels. The longer a fold gap, the greater the specific flow resistance in the fold. This is because the hydraulic fluid cannot flow unobstructed through the fold gap.
We have been able to implement the findings obtained from simulations into a practical application, and have confirmed them in numerous trials. Reducing a pressure loss in the filter element by as much as 40% at constant flow rate means it can increase up to 65% at a specified pressure loss. This also means, depending on application, smaller filters can be used to trim weight, resources, and costs. Also, reducing the pressure loss in existing systems means the bypass circuit (it protects the fine filter on cold startups) opens less often and for shorter periods. Consequently fewer particles get through the bypass to the clean-oil side and the danger of malfunction due to non-filtered oil significantly reduces.
The performance-optimized structure of a three-layer filter material consists of various fine glass and polyester fibers. This new material matrix in the pre-filter and ultra-fine filter materials significantly contribute to improved dirt-holding capacity. For example, the dirt holding capacity can be increased by as much as 60% in a 5 μm(c) filter.
The unusually low differential pressure and the high dirt holding capacity of the filter elements enable longer time between service and improves cold-start characteristics.
Elements of filter design
Depending on application, filter elements are subject to strong flexural-fatigue stresses induced by flow-rate fluctuations. These come from rpm fluctuations of drive motors, cylinder ratios, as well as the increasing use of variable displacement pumps in modern machines.
Conventional filter elements use a metal or plastic support fabric on the out-flow or clean-oil side. A support of metal also brings the advantage of electric conductivity, but has the danger of fatigue failure. Wire fatigue then leads to wire pieces in the hydraulic fluid. Some strength comes with plastic fabrics insensitive to flexural fatigue stresses. On their downside, such fabrics have extremely low electrical conductivity.
To counter these material-specific disadvantages, we use a hybrid fabric which has proven effective in years of application to support the filter material. The patented fabric consists of a mix of stainless steel and polyester fibers. This combination exploits all the advantages of metal and plastic fabrics and avoids the disadvantages of pure metal or plastic-only versions. Stainless-steel wire arranged longitudinally ensures complete dissipation of electrostatic charges, which prevents damage to the filter material and dirtier oil. The polyester fibers arranged transverse to the metal threads ensure optimal flexural fatigue strength and avoids of fatigue failure.
The structure of the filter material has been completely redesigned to contain multiple interlaminated filter and support layers. These use suitable laminating agents to improve the characteristics of the materials. In fact, it improves the differential-pressure stability of the filter material by a factor of three, relative to non-laminated materials.
In addition, a plastic sheathing shrink-fit onto the filter bellows ensures that they fit tightly on the perforated frame. This makes the filter element even more resistant to flexural fatigue-stress than conventionally manufactured filters. Improved fatigue characteristics, differential pressure stability, as well as safe dissipation of electrostatic charges significantly contribute to the long service life of the filter elements.
Optimizing filter fineness
It is also important, of course, to maintain a constant and high level of oil purity over the filter’s entire service period. To meet constantly increasing user requirements, and the ever-increasing complexity of hydraulic components, the new filter elements, with material designation 10EX2, allows improving the previous 12 μm(c) filter to 10 μm(c). For particles greater than 10 μm(c) this means a four-times higher separation capacity while simultaneously reducing pressure loss, as compared with the previous 12 μm(c) media.
Lastly, preventing knock-offs
The shrink-fit sleeve on the filter bellows improves its performance, gives it a modern look, and conveys the quality of the product. The sleeve is customer-specific and individually printed. Later, all EXAPOR MAX 2 filter elements will be fitted with this feature making it easy to identify. This means that original elements can be easily distinguished from knock-offs. Thus all machine operators who value quality and safety can easily verify the authenticity of the filter elements. WPE