Before choosing a filter element, we must first clarify two misunderstandings:
(1) Selecting a filter element with a certain precision (Xμm) can filter out all particles larger than this precision.
At present, the β value is usually used internationally to represent the filtration efficiency of the filter element. The so-called β value refers to the ratio of the number of particles larger than a certain size in the fluid at the inlet of the filter element to the number of particles larger than a certain size in the fluid at the outlet of the filter element. Therefore, the larger the β value, the higher the filtration efficiency of the filter element.
It can be seen that any filter element is a relative precision control, not an absolute precision control. For example, the filtering accuracy of PALL Corporation in the United States is calibrated when the β value is equal to 200. When choosing a filter element, in addition to filtration accuracy and filtration efficiency, the material and structural process of the filter element should also be considered, and products with high pressure collapse, high fluidity and long service life should be selected.
(2) The calibrated (nominal) flow rate of the filter element is the actual flow rate of the system.
In recent years, the selection data provided by the domestic filter element manufacturers rarely mention the relationship between the rated flow rate of the filter element and the actual flow rate of the system, which causes the system designer to have the illusion that the calibrated flow rate of the filter element is the actual flow rate of the hydraulic system. According to relevant information, the rated flow of the filter element is the flow rate of the oil passing through the clean filter element under the specified original resistance when the oil viscosity is 32mm2/s. However, in practical applications, due to the different media used and the temperature of the system, the viscosity of the oil will change at any time. If the filter element is selected according to the rated flow and the actual flow rate of 1:1, when the viscosity of the system oil is slightly larger, the resistance of the oil passing through the filter element increases (for example, the viscosity of No. 32 hydraulic oil at 0°C is about 420mm2/s) , Even reaching the value of the filter element’s pollution blockage, the filter element is considered to be blocked. Secondly, the filter element of the filter element is a wearing part, which is gradually polluted during work, the actual effective filtering area of the filter material is continuously reduced, and the resistance of the oil passing through the filter element quickly reaches the signal value of the pollution blocker. In this way, the filter element needs to be cleaned or replaced frequently, which increases the usage cost of the user. It will also cause unnecessary downtime or even stop production due to misleading maintenance personnel.
The higher the filtration precision of the hydraulic filter element, the better?
The high-precision filtration effect is indeed good, but this is actually a big misunderstanding. The precision of the hydraulic oil filter element required by the hydraulic system is not “high” but “appropriate”. High-precision hydraulic oil filter elements have relatively poor oil-passing ability (and the accuracy of hydraulic oil filter elements installed in different positions cannot be the same), and high-precision hydraulic oil filter elements are also more likely to be blocked. One is the short lifespan and must be replaced frequently.
Hydraulic oil filter selection steps
The general selection has the following steps:
①Find out the components most sensitive to contamination in the system, and determine the cleanliness required by the system;
②Determine the installation position, filtration form and pressure flow grade of the filter element;
③According to the set pressure difference and flow level, refer to the β value curve of various filter materials, and select the filter element material and length. Find out the shell pressure drop and filter element pressure drop from the sample chart, and then calculate the pressure difference, namely: △p filter element≤△p filter element setting; △p assembly≤△p assembly setting. Each filter element manufacturer in China has stipulated the rated flow rate of the filter element produced by them. According to the past experience and the usage of many customers, when the oil used in the system is general hydraulic oil, it is recommended that the filter element be selected according to the following multiples of flow rate. :
a The rated flow of the oil suction and oil return filters is more than 3 times the actual flow of the system;
b The rated flow of the pipeline filter element is more than 2.5 times the actual flow of the system. In addition, factors such as working environment, service life, component replacement frequency, and system selection media should also be properly considered to achieve the purpose of optimizing filter element selection.
Precautions for installation of hydraulic oil filter element
The installation location should be considered, which is also a very important part. If you are not sure where to install it, you cannot choose the hydraulic oil filter element. The function and accuracy of the hydraulic oil filter element in different positions are also different.
Post time: Mar-17-2022