How to choose hydraulic pressure filters?
The user must first understand the condition of their hydraulic system, and then select the filter. The selection goal is: long service life, easy to use, and satisfactory filtering effect.
Influencing factors of filter service lifeThe filter element installed inside the hydraulic filter is called the filter element, and its main material is the filter screen. The filter is mainly woven mesh, paper filter, glass fiber filter, chemical fiber filter and metal fiber filter felt. The filter media composed of wire and various fibers are very fragile in texture, although the manufacturing process for these materials is enhanced (such as: lining, impregnating resin), but there are still limitations in the working conditions. The main factors affecting the filter life are described as follows.
1. Pressure drop at both ends of the filterWhen the oil passes through the filter element, a certain pressure drop will be generated at both ends, and the specific value of the pressure drop depends on the structure and flow area of the filter element. When the filter element accepts impurities in the oil, these impurities will stay on the surface or inside the filter element, shielding or blocking some through holes or channels, so that the effective flow area is reduced, so that the pressure drop through the filter element is increased. As the impurities blocked by the filter element continue to increase, the pressure drop before and after the filter element also increases. These truncated particles will squeeze through the holes of the medium and re-enter the system; The pressure drop will also expand the original hole size, changing the performance of the filter element and reducing efficiency. If the pressure drop is too large, exceeding the structural strength of the filter element, the filter element will be flattened and collapsed, so that the function of the filter is lost. In order to make the filter element have sufficient strength within the working pressure range of the system, the minimum pressure that can cause the filter element to be flattened is often set as 1.5 times the working pressure of the system. This is, of course, when the oil must be forced through the filter layer without a bypass valve. This design often appears on high-pressure pipeline filters, and the strength of the filter element should be strengthened in the inner skeleton and lining network (seeiso 2941, iso 16889, iso 3968).
2. Compatibility of filter element and oilThe filter contains both metal filter elements and non-metal filter elements, which are the majority, and they all have the problem of whether they can be compatible with the oil in the system. These include the compatibility of chemical changes with changes in thermal effects. Especially in high temperature conditions can not be affected is more important. Therefore, various filter elements must be tested for oil compatibility at high temperatures (see ISO 2943).
3.The impact of low temperature workThe system operating at low temperatures also has an adverse effect on the filter. Because at low temperatures, some non-metallic materials in the filter element will become more fragile; And at low temperature, the increase of oil viscosity will cause the pressure drop to rise, which is easy to cause cracks in the medium material. In order to test the working condition of the filter at low temperature, the “cold start” test of the system must be carried out at the ultimate low temperature of the system. MIL-F-8815 has a special test procedure. China Aviation Standard HB 6779-93 also has provisions.
4. Periodic flow of oilThe flow of oil in the system is usually unstable. When the flow rate changes, it will cause the bending deformation of the filter element. In the case of periodic flow, due to the repeated deformation of the filter medium material, it will cause fatigue damage of the material and form fatigue cracks. Therefore, the filter in the design to ensure that the filter element has enough fatigue resistance, in the selection of filter materials should be tested (see ISO 3724).
Post time: Jan-20-2024