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How to correctly select hydraulic oil filter

October 19, 2021

Precautions for selecting hydraulic oil filter
In the hydraulic system, most of the failures are caused by hydraulic oil pollution and impurities mixed in the oil. Therefore, controlling the degree of oil pollution in the hydraulic system can basically ensure the normal and stable operation of the system. To prevent oil contamination in the hydraulic system, on the one hand, it is necessary to prevent external impurities from entering the hydraulic system, on the other hand, select a suitable hydraulic oil filter device to do a good job of filtering the hydraulic oil.

To prevent impurities from outside the hydraulic system from entering, the first thing to pay attention to is that the hydraulic oil tank is well sealed, and an air filter with good performance should be selected. Try to avoid direct contact with the external environment of the hydraulic oil. Before assembling the hydraulic system, thoroughly clean the oil tank, installation oil circuit, oil pipes and connecting parts to avoid residual machining iron filings. When injecting new hydraulic oil, it must be filtered before adding it to the oil tank.

The filter in the hydraulic system is an important device to remove impurities in the system and ensure the cleanliness of the hydraulic oil. Depending on the installation location and working environment, the following aspects should be paid attention to when selecting hydraulic oil filters:

At the suction port of the hydraulic oil pump, a filter with a slightly lower filtration accuracy and a large flow rate should be used. If the flow rate of the filter is insufficient, it is easy to cause cavitation at the suction port.

The filter installed in the hydraulic pipeline is generally located upstream of the more sensitive hydraulic components such as solenoid valves. And to ensure that the accuracy of the filter is higher than the clearance of the hydraulic components. At the same time, considering the pressure of the hydraulic system, select a filter device with sufficient pressure resistance.

The pressure resistance of the return oil filter is generally low. When selecting the type, the return oil flow of the hydraulic system should be fully considered to avoid the back pressure of the return oil due to the insufficient flow of the filter equipment.

In hydraulic systems, such as solenoid valves and other internal mechanically moving components, the clearance between the valve core and the valve body shoulder is very precise. Once small impurities enter the fitting gap, it is very easy to cause surface wear of the solenoid valve core during the reciprocating movement. Once the wear occurs, the surface gap increases, which will quickly lead to further serious friction, which can cause the solenoid valve to quickly Invalidate. Therefore, when selecting a hydraulic filter, it should fully meet the filtering accuracy requirements of hydraulic components.


Hydraulic oil filter element selection elements
The hydraulic oil filter element is a separate filter system that can be used in various oil systems to filter out solid impurities that are mixed in or generated inside the system during operation. It is mainly installed on the suction line, pressure oil line, return line, and bypass in the system. superior. The hydraulic oil filter element must meet the pressure loss requirements (the total pressure difference of the high-pressure filter is less than 0.1PMa, and the total pressure difference of the return oil filter is less than 0.05MPa) to ensure the optimization of the flow rate and the life of the filter element. So how to choose the right hydraulic oil filter element is very important.
1, filtration accuracy

First, determine the cleanliness level of the stains according to the needs of the hydraulic system, and then select the filter accuracy of the oil filter according to the cleanliness level according to the table. The hydraulic oil filter element commonly used in construction machinery has a nominal filtration degree of 10μm. Hydraulic oil cleanliness (ISO4406) filter element nominal filtration accuracy (μm) application range 13/103 hydraulic servo valve (using 3μm filter element) 16/135 hydraulic proportional valve (using 5μm filter element) 18/1510 general hydraulic components ( >10MPa) (using 10μm filter element) 19/1620 general hydraulic components (<10MPa) (using 20μm filter element)

Since the nominal filtration accuracy cannot truly reflect the filtration capacity of the filter element, the diameter of the large hard spherical particles that the filter can pass under the specified test conditions is often used as its filtration accuracy to directly reflect the initial filtration capacity of the new filter element. The main criterion for evaluating the hydraulic oil filter element is the β value measured according to ISO4572-1981E (multi-pass test), that is, the oil mixed with the standard test powder is circulated through the oil filter multiple times, and the particles on both sides of the oil inlet and outlet Ratio of numbers

2, flow characteristics

The flow rate and pressure drop of the filter element through the oil are important parameters of the flow characteristics. The flow characteristics test should be carried out according to the ISO3968-91 standard to draw the flow-pressure drop characteristic curve. Under the rated oil supply pressure, the total pressure drop (the sum of the pressure drop of the filter shell and the pressure drop of the filter element) should generally be less than 0.2MPa. Large flow: 400lt/min Oil viscosity test: 60to20Cst Low flow turbine: 0℃60lt/min High flow turbine: 0℃400lt/min

3, filter element strength

The rupture-impact test shall be carried out in accordance with the ISO2941-83 standard. The pressure difference that drops sharply when the filter element is damaged should be greater than the specified value.

4, flow fatigue characteristics

The fatigue test shall be in accordance with the ISO3724-90 standard. The filter element must undergo a fatigue test of 100,000 cycles.

5. Test of adaptability to hydraulic oil

The pressure flow endurance test should be carried out according to the ISO2943-83 standard to verify the compatibility of the filter material with the hydraulic oil.

The "filtration ratio b ratio" refers to the ratio of the number of particles larger than a given size in the fluid before filtration to the number of particles larger than the given size in the fluid after filtration. Nb=number of particles before filtration Na=number of particles after filtration X=particle size.