Selection of Hydraulic Filter Elements

Selection of Hydraulic Filter Elements

Hydraulic system design, power components, configuration control element is important, but reasonable selection of auxiliary elements of the filter element can not be ignored. Contamination of the hydraulic system against everywhere. It may be a gas, and solid objects can be metal particles and non-metallic particles, so the oil pollution control, will greatly reduce the failure of the hydraulic system, but the premise of the oil pollution is a hydraulic control system design the filter element is a reasonable selection and configuration. I participated in the hydraulic station commissioning, he had met the following conditions: (1) the boot time is very short, back to the oil filter on the sender more than tweet, replace the filter will not help. (2) the regulator set pressure when the system is difficult to remove the suction port filter fault disappears. After analysis, the two faults are filter selection issue, the former is the flow through the filter is too small, which is the suction filter is too delicate. Thus, the correct selection of the filter element is very important, it can improve the quality of the entire hydraulic system, but if the improper selection, also make frequent failure of the entire system, perform poorly.


1 hydraulic system filter selection


When the power components, control configuration element to determine the basic reference filter samples, according to the working conditions of the hydraulic system, sensitive to the oil, working pressure, load characteristics and environmental conditions, select the hydraulic system filter.


Before selecting a filter, we must first clarify two errors:


(1) Select a precision (Xμm) filter, it can filter out all particles larger than the precision.


At present, the commonly used β value to represent the international filter filtration efficiency, the so-called β value is the ratio of the number of particles of a certain size and number of particles at the outlet of the filter fluid filter inlet fluid larger than a certain size greater than. Therefore β value increases, the filtration efficiency of the filter is higher. and filtration efficiency β value table 1.



Table 1 β value with the filtration efficiency
β value Filtration efficiency β value Filtration efficiency

Table 1 β value with the filtration efficiency
β value Filtration efficiency β value Filtration efficiency
2 90% 200 99.5%
20 95% 500 99.8%
100 99% 1000 99.9%

Visible any filters are relative precision control, rather than absolute precision control. US companies such as PALL filtration accuracy is calibrated when β equals 200. When selecting a filter, in addition to considering filtration precision and filtration efficiency, we must also consider the structure of the filter material and technology, should be selected with a high pressure ulcer, high liquidity, long-life products.


(2) filter calibration (nominal) flow is the actual flow of the system.


In recent years, domestic filter selection information provided by manufacturers rarely mentioned relationship filter rated flow and the actual flow of the system, resulting in the selection system designers to produce the illusion that filter calibrated flow is the actual flow of the hydraulic system. Based on the data, filter the rated flow is the oil viscosity at 32 mm2 / s, the fluid under the provisions of the original resistance by clean filter traffic. However, in practice, due to different temperature systems and the use of different media, oil viscosity will change over time. If the rated flow rate and the actual flow rate of 1: 1 selection filter resistance increases when larger system fluid viscosity, the oil through a filter (such as hydraulic oil at 32 0 ℃, its viscosity of about 420 mm2 / s ), even to the clogging of the filter contamination sender transmission values, the filter was considered blocked. Second, the filter cartridge is part of wearing parts, work gradually be contaminated filter real effective filtration area continue to decrease, oil pollution clogging soon reach the sender transmit values ​​through the filter resistance. Thus, the filter needs frequent cleaning or replacing the filter, increase user costs. But also because of misleading cause unnecessary downtime maintenance personnel or even stop.


(3) Filtration higher the better.


As oil filter precision must be limited to between 80 to 120 mesh.


Its role is to limit the larger particles of contaminants into the oil pump and eliminate air bubbles.


(3) filter selection


General Selection has the following steps:


① by finding the most sensitive components of contamination, cleanliness determine system requirements;


② determine the installation position of the filter, the filter in the form of flow and pressure rating;


③ according to the set pressure and flow levels, reference β value curve of various filter, select the filter material, length. Isolated by the sample chart in the housing pressure drop and filter pressure drop, then accounting pressure, namely: △ p ≤ △ p cartridge filter setting; △ p ≤ △ p cartridge assembly set. When the filter domestic manufacturers are provided for the production of filters rated flow, based on past experience and the author of many customers, the system uses oil as general hydraulic oil, the proposed filter selection in the selection of the following flow multiples : ① suction, back to the oil filter rated flow system is more than three times the actual flow; ② line filter rated flow is 2.5 times more than the actual flow of the system. In addition, due consideration should work environment, life, element replacement frequency, the system selected media and other factors, to optimize filter selection purposes.


2 hydraulic system air filter Selection


Hydraulic system tank, since the oil supply, oil and media back to temperature changes, changes in the level of lifting occur at any time. Always in the process of air suction and exclusion, this is similar to “breathe” is closely related to the environment, in severe cases can lead to dirty air into the tank, pollution particles into the medium.


To prevent this, you must install the air filter in the fuel tank. Filtration precision air filter must match the filter system, so if the oil filter filtration system’s ability to 3μm, the air filter on the fuel tank must be 3μm. Selective air filter hydraulic station and working environment is related to when the environment is very bad, you can install a portable air filter in the air relatively clean location, set up a separate line connecting ventilation pipes. The lower the air flow air filter, and its ability to filter dirt better. So in the selection of the flux to have a certain margin, is generally used for the air flow rate is about 1.5 times the pump flow rate, air resistance should be less than 0.002 MPa.


In addition, the air cleaner filter element used must be replaced. Air intake above the fuel tank cap should be possible to prevent contaminants that accumulate at the top of the tank is sucked. Filter clogging indicator should be set to be guaranteed at all times to maintain and clean. The air-cleaner way should shield to prevent splashing of water into the tank.


3 Conclusions


Whether the correct selection and arrangement of the filter in the hydraulic system design, air filter, is the key to the hydraulic system of pollution control, but also to ensure safe and reliable operation. With the development of hydraulic technology, the hydraulic system of the hydraulic fluid cleanliness requirements have become more sophisticated, the hydraulic system design, not because it is auxiliary filter element and ignore it. In order for the system and components have an ideal working life, for medium pollution control is very important, a reasonable allocation of different types of filters, air filter. It is to meet a reliable guarantee the normal operation of the hydraulic system.

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