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Hydraulic oil filter element in the hydraulic system, used to filter the working medium, solid particles and colloidal substances. As well as filter out a variety of oil systems from the outside mixed or the system in the operation of the internal solid impurities, it can effectively control the degree of pollution of the working medium, protect the normal work of mechanical equipment, is the best part of the pipeline series of transport media. So what are the requirements of the hydraulic system for the filter The hydraulic oil filter element is mainly installed in the hydraulic system: on the oil suction circuit, on the pressure oil circuit, on the return pipeline, on the bypass, and on the separate filtration system. 1, the oil filter is used to protect the hydraulic components of the system, so that it is not damaged by pollution particles. However, it also increases the oil absorption resistance of the pump, so it is necessary to choose large flow capacity, high filtration efficiency, large scale capacity, and small pressure loss. Such as mesh and line gap filters. Filtration accuracy and efficiency is a contradiction, the accuracy of the filter is generally selected 80-200μm, to meet the needs of the line. If it is a plunger pump, you can even consider not applying a filter. 2, the pressure oil filter, its purpose is to protect other hydraulic parts other than the pump, due to the high pressure installation position, should first consider high pressure resistance. If it is used to protect components with poor anti-pollution ability (such as servo valves), it is necessary to consider the filtration accuracy and flow capacity, and it is recommended to use a high-pressure oil filter with a housing. 3. The return pipe passes through the filter, and its purpose is to filter out the dirt in the system before returning the system oil to the tank to ensure that the oil in the tank is clean. The filtration accuracy is generally 10-50μm. In this filtration method, the filter may be blocked, which in turn blocks the hydraulic components of the system. A return filter with a bypass valve is recommended. In addition, when the oil is suddenly switched on at high pressure, there will be an impact, so a filter with a large flow rate should be selected. If the pressure is too large, the back pressure valve should be added to protect the filter. 4, bypass filter, the filter is a filter composed of filters and small pumps independent of the hydraulic system outside the filter device, not affected by the system. For the main system of variable pump, the use of this filtration method can compensate for the reduction of filtration capacity at low flow rates. The bypass filter generally selects about 20% of the main system pump flow rate (max), and the filter accuracy is high.

In daily life, whether it is in industry or in life, filter equipment is inseparable, but we rarely pay attention to these. However, in the industrial implementation of production operations, filtration equipment is used in all aspects. In the hydraulic filtration equipment, what is the importance of the filter?     With the development of science and technology, modern manufacturing technology is more and more towards the direction of fast, high pressure, high precision, high automation and reliability, and the power transmission part of mechanical equipment is more and more common to use hydraulic equipment to achieve various actions. The application of precision hydraulic components such as axial piston pump, proportional valve, servo valve and hydrostatic hydraulic bearing in hydraulic system is more and more popular. The normal operation of such components has strict requirements for oil cleanliness. A large proportion of system failures are attributed to contaminants in the system.       Contaminants in hydraulic systems refer to various substances in the oil that are harmful to system reliability and component life. There are mainly the following categories: solid particles, water, air, chemicals and so on. Relevant data show that in the hydraulic system failure caused by pollution, except for a small part of corrosion, the rest are due to the presence of solid particles caused by mechanical wear on the surface of hydraulic components.   Therefore, it is very important to install filtration equipment in the hydraulic system, which can not only reduce the number of equipment failures, but also extend the service life of the equipment and reduce the cost. The most common filter elements are hydraulic oil filters, filters, and oil filters. We can adjust the filter equipment according to the installation of our own equipment. Can filter out the wear debris and oil mist impurities to a certain extent, not only can purify the filter medium, but also improve the work efficiency.

1, installed in the pump suction port. Install A mesh or line-gap filter at the oil suction port of the pump to prevent large particles of impurities from entering the pump, while having a high flow capacity to prevent cavitation, as shown in FIG. 1 in A.   2, installed in the pump outlet. As shown in Figure A (2), the outlet of the pump can protect components other than the pump, but it is necessary to select a filter with high filtration accuracy and can withstand the working pressure and impact pressure on the oil circuit, and the pressure loss is generally less than 0.35MPa. This method is often used in filtration systems with high accuracy requirements and before servo valves and speed regulating valves to ensure their normal operation. In order to protect the filter itself, a filter with a blocking transmitter should be selected.     Installation position of the filter   3. Installed on the oil return circuit of the system. Installed in the oil return circuit can filter the oil before returning to the tank into the system or system generated dirt. Due to the low oil return pressure, the filter with low filter element strength can be used, and its pressure drop has little impact on the system. In order to prevent the filter from blocking, it is generally connected to the filter with A safety valve or install a blocking signaling device, as shown in Figure A (3).   4. Install it on the bypass of the system. As shown in FIG. A (4), the filter is connected to the valve in parallel so that the oil in the system is continuously purified.   5, installed on the independent filter system. In the large hydraulic system, an independent filtration system composed of hydraulic pump and filter can be specially designed to filter the dirt in the hydraulic system tank, and improve the cleanliness of the oil through continuous circulation. The special filter truck is also an independent filter system, as shown in Figure A, 5.   When using the filter, it should also be noted that the filter can only be used one-way and installed in accordance with the specified liquid flow direction to facilitate the cleaning and safety of the filter element. When cleaning or replacing the filter element, it is necessary to prevent external pollutants from invading the hydraulic system.

introduction   Hydraulic filter as the main component of hydraulic system pollution control, its design and selection is reasonable, daily use (maintenance) is correct is directly related to the safety and reliability of the system. In practical applications, many users still have many misunderstandings about the selection and use of filters, which will affect the normal and reliable work of the hydraulic system if not corrected.   1 Filter selection errors in hydraulic system   1.1 Misunderstanding 1: Choosing a high-precision oil suction filter can both effectively protect the pump and ensure the cleanliness of the system   Because the particle pollutants in the oil will aggravate the wear of the pump and thus affect the performance and life of the pump, large particle pollutants may also jam the pump, seriously affecting the safety and reliability of the system. Therefore, some users choose high-precision oil suction filters, thinking that it can protect the pump and ensure the cleanliness of the system. However, the high-precision oil suction filter is easy to clog due to excessive pollutants, resulting in poor pump oil absorption, resulting in suction, accelerating pump wear, and seriously affecting system safety. Therefore, the pressure drop of the oil suction filter should be strictly controlled. General hydraulic systems can consider installing low-precision oil suction filters to protect the pump, and install filters in front of contaminant-sensitive components to protect them to control the impact of particle pollution. In order to most effectively intercept contamination in the loop due to component wear or external intrusion, it is recommended to install a return oil filter to control it to improve the cleanliness of the entire system. At the same time, pipelines and fuel tanks should be thoroughly cleaned before the operation of the system to ensure the degree of oil pollution. In this way, the oil pollution of the whole system is basically controlled, which protects the pump and the whole system.   1.2 Misunderstanding two: The rated (nominal) flow of the filter is the actual flow of the system       The rated flow rate of the filter is the flow rate through the clean filter element under the specified original resistance when the oil viscosity is 32cst. However, in practical applications, due to the different media used and the different temperature of the system, the oil viscosity will also change at any time. If the filter is selected according to the rated flow rate and the actual flow rate 1:1, when the viscosity of the system oil is slightly larger, the resistance of the oil through the filter will increase (such as the viscosity of No. 32 hydraulic oil at 0 ° C is about 420cst), and even reach the pollution blocking signal value of the filter, and the filter element is considered blocked. Secondly, the filter element of the filter is a wearing part, the work is gradually polluted, the actual effective filtration area of the filter material is constantly reduced, and the resistance of the oil through the filter soon reaches the pollution blocking signal value. In this way, the filter needs to be cleaned or replaced frequently, increasing the user's cost.   At present, the domestic filter manufacturers have stipulated the rated flow of their filter production, according to the author's previous experience and many customers use, the system uses oil for general hydraulic oil, it is recommended that the filter in the selection of the following multiple of the flow :① the rated flow of the oil suction, return oil filter is more than 3 times the actual flow of the system; The rated flow rate of the pipeline filter is more than 2.5 times the actual flow rate of the system. If the oil is not general hydraulic oil or high viscosity hydraulic oil, please consult the manufacturer for selection.   1.3 Misunderstanding 3: The higher the accuracy of the filter selection, the better   The solid pollution in the hydraulic system is the main reason for the failure of the hydraulic system, so the high-precision filter is selected to control the pollution. In fact, this not only increases the manufacturing cost of the system, but also shortens the service life of the filter element. Then how to choose the accuracy of the filter reasonably? It is mainly determined by the pollution requirements of the components of the hydraulic system on the oil, and the higher the cleanliness of the components, the higher the precision of the filter selection.   When the wear particles enter the gap between the moving pairs of the components, a chain reaction of wear will occur. So wear it down To minimize and maximize the life of the component, it is necessary to filter out particles that are close to the gap size. The level of oil contamination required for typical hydraulic components and the recommended value of filter selection accuracy are shown in Table 1.   picture   1.4 Misconception four :(Xμm) filter element with filtration accuracy can filter out all particles greater than its accuracy   Because the hydraulic pollution control technology is still in the development stage in our country, many users are not very understanding of the definition of filter precision, that the system as long as the installation of (Xμm) precision filter can ensure that there are no pollutants greater than (Xμm) particles in the system oil, in fact, this is wrong. The national standard GB/T20079-2006 stipulates that the filtration capacity of the filter is expressed by the filtration ratio βx(c), which is defined as the ratio of the number of pollutant particles in the unit volume of the oil above and below the filter that is greater than a given size x(c).   That is, the filtration accuracy is defined as the minimum particle size x(c) that can be effectively captured by the filter (βx(c)≥100), in microns as a unit of measurement, expressed in μm. At present, the size of the filter ratio βx(c) value is not uniform among filter manufacturers. Since the filtration accuracy is determined according to the filtration ratio, the same filtration accuracy is completely different because of its actual βx value. Therefore, the filter element with (Xμm) filtration accuracy can not completely filter out particles greater than its accuracy. If the system selects a filter with a smaller filtration value than βx, the oil pollution degree is difficult to control.   2 Daily use (maintenance) filter misunderstandings   2.1 Misunderstanding 1: The filter with a bypass valve can not be cleaned or replaced for a long time after the filter element is blocked   Many users will think that the bypass valve of the filter and the safety valve of the system have the same function: after the filter element is blocked, the bypass valve is opened, and the full flow of the system oil passes through, which has no effect on the system. When the bypass valve of the filter is opened, the pollutants blocked by the filter element (the filtered pollution particles) will re-enter the system through the bypass valve, and the pollution concentration of the local oil is the highest at this time, which has great damage to the hydraulic components, and the previous pollution control will lose meaning. Unless the system requires very high continuity of work, it is best to choose a filter without a bypass valve. Even if a filter with a bypass valve is selected, when the pollution of the filter blocks the transmitter, it is necessary to clean or replace the filter element in time, which is the way to ensure the safe and reliable operation of the system.   2.2 Misunderstanding 2: To judge the filter performance by the service life of the filter Many users because there is no oil pollution detection equipment, to judge the filter performance by the service life of the filter. The filter plugging speed shows the good and bad performance, and these two ideas are one-sided. Because the filter performance of the filter is mainly reflected by the filter ratio, pollution capacity, original pressure loss and other performance indicators, only in the same working conditions and to ensure the cleanliness of the hydraulic system requirements, the longer the service life, the better. 3 Closing remarks   Whether the filter can be correctly selected and used in the hydraulic system is the key to the pollution control of the hydraulic system, and also the reliable guarantee of the safe operation of the system. In order to make the system and components have an ideal working life, it is necessary to carry out pollution control on the oil, configure reasonable different types of filters to achieve the most economical and reliable effect, and perform good daily maintenance on the filter to ensure the safe and reliable operation of the system

Hydraulic filter as the main component of hydraulic system pollution control, its design and selection is reasonable, daily use (maintenance) is correct is directly related to the safety and reliability of the system. In practical applications, many users still have many misunderstandings about the selection and use of filters, which will affect the normal and reliable work of the hydraulic system if not corrected.   1 Filter selection errors in hydraulic system   1.1 Misunderstanding 1: Choosing a high-precision oil suction filter can both effectively protect the pump and ensure the cleanliness of the system   Because the particle pollutants in the oil will aggravate the wear of the pump and thus affect the performance and life of the pump, large particle pollutants may also jam the pump, seriously affecting the safety and reliability of the system. Therefore, some users choose high-precision oil suction filters, thinking that it can protect the pump and ensure the cleanliness of the system. However, the high-precision oil suction filter is easy to clog due to excessive pollutants, resulting in poor pump oil absorption, resulting in suction, accelerating pump wear, and seriously affecting system safety. Therefore, the pressure drop of the oil suction filter should be strictly controlled. General hydraulic systems can consider installing low-precision oil suction filters to protect the pump, and install filters in front of contaminant-sensitive components to protect them to control the impact of particle pollution. In order to most effectively intercept contamination in the loop due to component wear or external intrusion, it is recommended to install a return oil filter to control it to improve the cleanliness of the entire system. At the same time, pipelines and fuel tanks should be thoroughly cleaned before the operation of the system to ensure the degree of oil pollution. In this way, the oil pollution of the whole system is basically controlled, which protects the pump and the whole system.   1.2 Misunderstanding two: The rated (nominal) flow of the filter is the actual flow of the system       The rated flow rate of the filter is the flow rate through the clean filter element under the specified original resistance when the oil viscosity is 32cst. However, in practical applications, due to the different media used and the different temperature of the system, the oil viscosity will also change at any time. If the filter is selected according to the rated flow rate and the actual flow rate 1:1, when the viscosity of the system oil is slightly larger, the resistance of the oil through the filter will increase (such as the viscosity of No. 32 hydraulic oil at 0 ° C is about 420cst), and even reach the pollution blocking signal value of the filter, and the filter element is considered blocked. Secondly, the filter element of the filter is a wearing part, the work is gradually polluted, the actual effective filtration area of the filter material is constantly reduced, and the resistance of the oil through the filter soon reaches the pollution blocking signal value. In this way, the filter needs to be cleaned or replaced frequently, increasing the user's cost.   At present, the domestic filter manufacturers have stipulated the rated flow of their filter production, according to the author's previous experience and many customers use, the system uses oil for general hydraulic oil, it is recommended that the filter in the selection of the following multiple of the flow :① the rated flow of the oil suction, return oil filter is more than 3 times the actual flow of the system; The rated flow rate of the pipeline filter is more than 2.5 times the actual flow rate of the system. If the oil is not general hydraulic oil or high viscosity hydraulic oil, please consult the manufacturer for selection.   1.3 Misunderstanding 3: The higher the accuracy of the filter selection, the better   The solid pollution in the hydraulic system is the main reason for the failure of the hydraulic system, so the high-precision filter is selected to control the pollution. In fact, this not only increases the manufacturing cost of the system, but also shortens the service life of the filter element. Then how to choose the accuracy of the filter reasonably? It is mainly determined by the pollution requirements of the components of the hydraulic system on the oil, and the higher the cleanliness of the components, the higher the precision of the filter selection.   When the wear particles enter the gap between the moving pairs of the components, a chain reaction of wear will occur. So wear it down To minimize and maximize the life of the component, it is necessary to filter out particles that are close to the gap size. The level of oil contamination required for typical hydraulic components and the recommended value of filter selection accuracy are shown in Table 1.   picture   1.4 Misconception four :(Xμm) filter element with filtration accuracy can filter out all particles greater than its accuracy   Because the hydraulic pollution control technology is still in the development stage in our country, many users are not very understanding of the definition of filter precision, that the system as long as the installation of (Xμm) precision filter can ensure that there are no pollutants greater than (Xμm) particles in the system oil, in fact, this is wrong. The national standard GB/T20079-2006 stipulates that the filtration capacity of the filter is expressed by the filtration ratio βx(c), which is defined as the ratio of the number of pollutant particles in the unit volume of the oil above and below the filter that is greater than a given size x(c).   That is, the filtration accuracy is defined as the minimum particle size x(c) that can be effectively captured by the filter (βx(c)≥100), in microns as a unit of measurement, expressed in μm. At present, the size of the filter ratio βx(c) value is not uniform among filter manufacturers. Since the filtration accuracy is determined according to the filtration ratio, the same filtration accuracy is completely different because of its actual βx value. Therefore, the filter element with (Xμm) filtration accuracy can not completely filter out particles greater than its accuracy. If the system selects a filter with a smaller filtration value than βx, the oil pollution degree is difficult to control.   2 Daily use (maintenance) filter misunderstandings   2.1 Misunderstanding 1: The filter with a bypass valve can not be cleaned or replaced for a long time after the filter element is blocked   Many users will think that the bypass valve of the filter and the safety valve of the system have the same function: after the filter element is blocked, the bypass valve is opened, and the full flow of the system oil passes through, which has no effect on the system. When the bypass valve of the filter is opened, the pollutants blocked by the filter element (the filtered pollution particles) will re-enter the system through the bypass valve, and the pollution concentration of the local oil is the highest at this time, which has great damage to the hydraulic components, and the previous pollution control will lose meaning. Unless the system requires very high continuity of work, it is best to choose a filter without a bypass valve. Even if a filter with a bypass valve is selected, when the pollution of the filter blocks the transmitter, it is necessary to clean or replace the filter element in time, which is the way to ensure the safe and reliable operation of the system.   2.2 Misunderstanding 2: To judge the filter performance by the service life of the filter Many users because there is no oil pollution detection equipment, to judge the filter performance by the service life of the filter. The filter plugging speed shows the good and bad performance, and these two ideas are one-sided. Because the filter performance of the filter is mainly reflected by the filter ratio, pollution capacity, original pressure loss and other performance indicators, only in the same working conditions and to ensure the cleanliness of the hydraulic system requirements, the longer the service life, the better. 3 Closing remarks   Whether the filter can be correctly selected and used in the hydraulic system is the key to the pollution control of the hydraulic system, and also the reliable guarantee of the safe operation of the system. In order to make the system and components have an ideal working life, it is necessary to carry out pollution control on the oil, configure reasonable different types of filters to achieve the most economical and reliable effect, and perform good daily maintenance on the filter to ensure the safe and reliable operation of the system

As we all know, most of the failures of the hydraulic system are caused by oil pollution, so the filter plays an important role in the hydraulic system. As a hydraulic designer, choosing a filter is sometimes a headache. Because, no matter what brand of filter, there are many kinds, and the various parameters and curves on the sample are confusing. Today, Xiaobian share a little experience in the selection of filters.       Let's figure out where you need a filter in your hydraulic system.   l Oil suction filter   l pump outlet high pressure filter   l Return oil filter   l Bypass filter   l Special filter for key parts         The above filters are not necessarily used at the same time, and different industries may choose different options.   Oil suction filter: Generally a very low precision filter, can directly protect the pump. In general, unless the oil accuracy management is poor, it will be used, because, normally, the oil in the protective tank with the return oil filter will never have too much impurities, unless the tank is open. Oil suction filter is not recommended now, because it has a great impact on the suction of the pump, and it is completely unnecessary.   Pump outlet high pressure filter: High pressure is a major feature, here the filter must be resistant to high pressure, and should be higher than the system pressure a grade. The oil pumped out is directly into each control valve, so the cleanliness of the oil must be able to ensure the needs of the system, so the filter here is very important.   Oil return filter: oil cylinder, motor, valve, etc. will produce wear impurities in the work, as well as maintenance, pipeline reconnection and other external impurities. The return oil filter is to filter out these impurities. It is characterized by low pressure, large flow and low filtration accuracy.   Bypass filter: Independent filtration system, specially used for cleaning or cooling oil. Generally, the filtration accuracy is relatively high.   Special filter for key parts: Generally, the filter is added separately before the valve or actuator with higher cleanliness requirements, and the accuracy is higher.   Filter selection procedure   1. First determine the filter form and pressure level according to the use position.   Use location   Pump outlet   Oil return   by-pass   Key position   Pressure rating   1.5 times the working pressure   1.6MPa, 2.5MPa   1.5 times the working pressure   1.5 times the working pressure   type   Pipeline type, side plate, top plate. monocular   Insert type, floor type. Single or double barrel   Insert type, floor type. Single or double barrel   Pipeline type, side plate, top plate. monocular   2. Select the appropriate filtration accuracy according to the cleanliness required by the system. This depends on the type of filter configured for the specific system.   For example, the cleanliness of the rolling hydraulic system requires NAS6, and the pump outlet + oil return + by-pass filter combination can be selected. Pump outlet 10 microns, oil return 20 microns, bypass 3 microns.   3. Then it is time to select the specific model with the manufacturer's sample.   There are many models of each manufacturer, and the specific choice should refer to the experience of predecessors and the technical support of manufacturers.   Almost every manufacturer will give the pressure difference curve of the filter, which will always make people confused. Here are some lessons to share. picture   When you determine which type of filter to use, then determine the maximum flow rate of the filter in the system, and then find out in the curve how much is the pressure difference of the different specifications of the filter under this flow rate, and then find out the pressure difference of the filter housing, the two sum is the overall maximum pressure difference of the filter.   △P total =△P shell +△P filter element   Of course, there is also a relationship between viscosity, so the real pressure difference should be multiplied by a coefficient, which is the viscosity of the oil used in the system divided by the viscosity of the sample curve.   In what range is this total pressure difference appropriate:     Pump outlet/bypass/Key position filter: △P total ≤1bar;   Others: △P total ≤0.05bar;     4. Some auxiliary functions should be selected according to the specific situation.   Blocking alarm: mechanical visual, light visual, signal remote transmission and so on.   Bypass check valve opening pressure.

Why does the hydraulic oil filtration of the hydraulic station play a vital role?   When selecting the main filter of the hydraulic station, the determination of its accuracy should consider the degree of oil pollution that the key components in the system can withstand, the system's pollutant intrusion rate and working conditions and other factors. Starting from the pollution damage control point, the accuracy of the filter should be able to effectively filter out particles whose size is close to the dynamic oil film thickness of the moving pair of components. Because once the particles of this size enter the gap of the moving pair, it will cause the surface wear of the component, and increase the gap, so that the larger particles enter the gap, introduce a step of wear, resulting in a "chain reaction" of severe wear, resulting in the failure of the component.       The selection principle of hydraulic station filter: When selecting a filter, the following performance requirements should be considered:   (1) It has a large enough oil flow capacity and small pressure loss;   (2) The filtration accuracy should meet the design requirements;   (3) The filter element has sufficient strength and contaminant capacity;   (4) the filter element has good corrosion resistance and can work for a long time at the specified temperature;   (5) The replacement, cleaning and maintenance of the filter element is convenient.

The main function of the filter is to control the pollution level of the hydraulic system, ensure the normal working performance of the system, and extend the service life of the components. The selection of filters with low filtration accuracy or little maintenance of filters will lead to excessive pollution of the system, making the system unreliable or damaged hydraulic components. The performance of the filter mainly depends on two aspects, on the one hand, the ability to filter pollutants, that is, the filtration accuracy; On the other hand, it includes scale capacity, pressure drop and flow capacity. The correct selection of filters requires careful evaluation according to the technical requirements of the entire hydraulic system and the characteristics of the various types of filters. picture   The selection of the filter includes the selection of the filter type, the selection of the specification and the determination of the installation position of the filter in the loop. Among them, when selecting the filter model, first select the appropriate filter type according to the design requirements of the hydraulic system, and then select the appropriate filter model and specification according to the filtration accuracy. In addition, the following points should be considered: ① The filter can maintain sufficient flow capacity for a long time; ② The filter element has sufficient strength and is not damaged by the effect of oil pressure; ③ Good corrosion resistance of filter element; ④ the filter element can work continuously at the specified temperature; ⑤ The filter element is easy to clean and replace. In addition to the selection of filtration accuracy, it is also necessary to determine the location of the filter installation according to the pollution sensitivity of the hydraulic system and components and the type of filter selected, so that the degree of oil contamination is as low as possible. The filter can be installed in various positions in the hydraulic system, such as the oil suction and discharge ports of the hydraulic pump, the oil inlet and outlet ports of the actuator, and the oil inlet of the sensitive element, as shown in Figure 36. The high-pressure filter should be used at the oil inlet of the hydraulic pump, the actuator and the sensitive element, and the low-pressure filter can be used at the system oil return port and the oil suction port of the hydraulic pump. The pressure drop of the filter at the suction port of the hydraulic pump should be as low as possible to avoid affecting the self-priming capacity of the hydraulic pump.     picture   1- oil suction filter; 2- Oil injection port/air filter; 3- Oil suction filter with bypass valve; 4- High pressure filter with bypass valve; 5, 6-high pressure filter; 7- Low pressure oil return filter with bypass valve; 8- Low pressure filter with bypass valve independent of main hydraulic system

The filter is very important to keep the hydraulic system clean and extend the service life of the hydraulic system. How to choose the right filter? picture     Each machine and component in the hydraulic system has its own set of requirements, each of which affects each other and, of course, the selection of filters. To determine the size of the filter and select the right filter, you must understand the following five key pieces of information: 01 Filter performance requirements   The performance requirements of the filter are usually expressed in terms of the overworry ratio β, which is the ratio of particles entering the filter to particles exiting the filter. Today's hydraulic filters are designed with a medium that captures and holds more pollution particles than ever before, reducing pressure drop and extending service life. For example, applications that require high-performance components will typically have an overworry ratio β of more than 1000 (i.e., 1000 particles enter the filter and only one particle passes through). picture     02 Hydraulic system   After determining the performance requirements of the filter, we need to be clear about the hydraulic components installed in the hydraulic system circuit, according to industry standards, these hydraulic components need to have the corresponding standard filter type. This standard drives the ISO cleanliness code requirements and helps determine the right filter element type. For example, a proportional valve in a loop may require a 20/18/15 ISO cleanliness code, and in order to meet the standards set by the ISO code, the circuit needs a filter with 3 µm or 6 µm absolute filtration. When choosing the size of the filter, it is also necessary to consider the pollution capacity, pressure drop, cost and other factors, to understand what hydraulic components are attached to the filter, and to understand how these hydraulic components affect the performance requirements of the filter, which can save costs. picture     03 Oil viscosity     The viscosity of the oil has a great influence on the size of the filter. When choosing a filter, many people tend to ignore this factor, often choosing a larger filter than the actual need, resulting in higher operating costs. The filter size is too small and the pressure drop is too high, resulting in premature tripping of the blockage indicator. If the filter size is too large, it will lead to high cost, large footprint and high replacement cost. We should fully understand the normal temperature range of the hydraulic system, according to the accurate minimum temperature to select the filter.   04 Understand the blockage indicator   Assuming that the filter of the system has a clogging indicator (analog or digital), the user should have a suitable target for the pressure drop when selecting the filter size. picture         Typically, the pressure difference for the plugging indicator ranges from 1 to 8 bar, and the ratio of the plugging indicator setting to the clean pressure drop is at least 3:1. For example, assuming the filter has a 5 bar clogging indicator, the acceptable maximum clean pressure drop target is about 1.7 bar based on a 3:1 ratio. Without understanding this principle, we may mistakenly choose the size of the filter. While too large a filter can ensure the highest amount of protection, it will increase the cost.   05 Understand the flow   When choosing the size of the filter, the flow rate must be considered, and we need to consider the maximum flow rate. Note that intermittent flow may exceed the maximum flow of the pump. For example, in an accumulator loop, where the accumulator stores a certain amount of pressurized fluid and releases it into the system to supplement the pump flow, the flow through the pressure filter connected downstream of the accumulator should take into account this additional flow. Underestimating the flow through the filter increases the pressure drop through the filter element, increasing operating and maintenance costs.

Filter selection principle requirements Filter is a small device to remove a small amount of solid particles in the liquid, which can protect the normal work of the equipment, when the fluid enters the filter cartridge with a certain specification filter screen, the impurities are blocked, and the clean filtrate is discharged by the filter outlet, when it needs to be cleaned, as long as the detachable filter cartridge is removed and re-loaded after treatment.       1, filter inlet and outlet diameter: In principle, the inlet and outlet diameter of the filter should not be smaller than the inlet diameter of the matching pump, generally consistent with the inlet pipe caliber.       2, nominal pressure selection: Determine the pressure level of the filter according to the highest possible pressure in the filter line.       3, the selection of the number of holes: The selection of filter hole number mainly considers the particle size of the impurities to be intercepted, according to the process requirements of the medium process. The particle size of various specifications can be intercepted by the screen check the table "filter specifications".       4, filter material: The material of the filter is generally the same as the material of the connected process pipe, and the filter of cast iron, carbon steel, low alloy steel or stainless steel can be considered for different service conditions.       5, filter resistance loss calculation Water filter, in the general calculation of rated flow rate, the pressure loss is 0.52 ~ 1.2kpa.     Filter application 1. Stainless steel filter Stainless steel filters are widely used in steam, air, water, oil, and other media pipelines; Protect all kinds of equipment, pumps, valves, etc.; Free from rust, welding and other impurities in the pipeline, caused by blockage and damage. Stainless steel filter has strong pollution resistance, convenient sewage discharge, large circulation area, small pressure loss, simple structure, small volume, light weight. Filter material is stainless steel, strong corrosion resistance, long service life.       2. Y-type filter Y-type filter is an indispensable filter device in the pipeline system of conveying media. Y-type filter is usually installed at the inlet end of pressure reducing valve, pressure relief valve, fixed level valve or other equipment to remove impurities in the medium to protect the normal use of valves and equipment. Y-type filter has the characteristics of advanced structure, low resistance, convenient blowdown and so on.       3. Y-type drag rod telescopic filter Y-type telescopic filter adopts a new design, the combination of Y-type filter and telescopic joint, simple structure, easy to use, to solve a variety of different standard products flange length caused by different fixed pipe installation inconvenience defects, telescopic filter is mainly used in high-rise construction, multi-storey buildings or factories in the water supply and drainage piping. Usually installed in the pressure reducing valve, pressure relief valve, fixed level valve or other main equipment inlet end, the installation of the rod telescopic filter is easy to cut the pipeline debris or installation and disassembly to ensure the normal use of valves or equipment.       4. Basket filter The basket filter removes small equipment containing a small amount of solids in the liquid, which can protect the normal operation of compressors, pumps and other equipment and instruments; It is also a small equipment to improve product purity and purify gas. Therefore, the basket filter is widely used in petroleum, chemical, chemical fiber, medicine, food and other industries. The basket filter is composed of a shell, a blowdown cover, a filter element, a filter screen, a bolt, etc.       5. T-type filter T-type filter is widely used in the pipeline of steam, air, water, oil and other media, to protect various equipment on the pipeline system, such as pumps, valves, etc., from the rust in the pipeline, welding slag and other debris to bring blockage and damage to the pipeline. The T-type filter produced by Shanghai Rimei Valve Manufacturing Co., Ltd. has the characteristics of strong anti-fouling performance, convenient blowdown, large circulation area, small pressure loss, simple structure, small volume and so on. The filter material of T-type filter is stainless steel, strong corrosion resistance, long service life; T-type filter is also divided into straight flow and fold flow, the density of the filter screen is 10-120 mesh, the temperature is 0~450℃, can be selected according to user needs.

Analysis: The filter in the water treatment industry mainly has quartz sand filter, activated carbon filter, multi-media filter, bag filter and so on. Quartz stone filter     Quartz sand mechanical filter is the use of quartz sand as a filter medium, under a certain pressure, the high turbidity of water through a certain thickness of granular or non-granular quartz sand filtration, effective interception to remove suspended matter in the water, organic matter, colloid particles, microbial chlorine, odor and some heavy metal ions, so that the water clarification of the water treatment device. According to different water production, need to be equipped with different mesh number (different diameter of quartz sand particles), it and activated carbon composed of activated carbon filter, with sand 枃 into the removal of iron spade filters are collectively referred to as quartz sand filter.     Multimedia filter Multi-media filter, are used for water treatment turbidity, softened water, and pure water of the pre-stage multi-media filter (filter bed), both the use of more than two media as a filter layer of the media filter, in the industrial circulating water treatment system, to remove impurities in sewage, adsorption oil, so that the water quality in line with the requirements of recycling. The role of filtration is mainly to remove suspended or colloidal impurities in water, especially to effectively remove tiny bacteria that cannot be removed by precipitation technology, BOD5 and COD also have a certain degree of removal effect.           Activated carbon filter The activated carbon filter uses granular activated carbon to further remove the residual chlorine, organic matter and suspended matter impurities in the effluent of the mechanical filter, providing good conditions for subsequent reverse osmosis treatment.       The activated carbon filter mainly uses activated carbon organic flocculants with high carbon content, large molecular weight and large specific surface area to physically adsorb impurities in water to meet the water quality requirements. When the water flows through the pores of activated carbon, various suspended particles and organic matter are adsorbed in the activated carbon pores under the action of van der Waals force; At the same time, the chlorine (hypochlorous acid) adsorbed on the surface of the activated carbon has a chemical reaction on the surface of the carbon and is reduced to chloride ions, thus effectively removing chlorine and ensuring that the residual chlorine in the effluent is less than 0.1ppm, meeting the operating conditions of the RO membrane. Over time, the retention of activated carbon in the pores and between the particles gradually increases, so that the pressure difference between the front and back of the filter increases until it fails. Under normal circumstances, according to the pressure difference before and after the filter, the filter material is backwashed by the reverse water flow, so that most of the intercepts adsorbed in the activated carbon pores are stripped and taken away by the water flow, and the adsorption function is restored; When the activated carbon reaches the saturated adsorption capacity and completely fails, the activated carbon should be regenerated or replaced to meet the engineering requirements.       The surface area of activated carbon has strong physical adsorption capacity. Activated carbon filter device is to use activated carbon as a filter medium, the use of activated carbon itself has adsorption and decolorization ability, remove impurities in the liquid, so that the liquid is purified. It is often used in the pre-treatment of reverse osmosis equipment and the filtration of groundwater, sewage and other suspended solids. Widely used in food, medicine, electronics, chemical, industrial wastewater and other industries in the water treatment project is the pretreatment equipment in the water treatment process, used to prevent water pollutants on the subsequent equipment pollution, can also be used to improve the smell and color of water. The activated carbon filter mainly uses the adsorption and decolorization ability of activated carbon itself to remove impurities in the liquid and purify the liquid       Precision filter     Precision filters (also known as security filters) are mostly made of stainless steel shell, internal filter elements (such as PP cotton), mainly used in multi-media pre-treatment filtration, reverse osmosis, ultrafiltration and other membrane filtration equipment before. It is used to filter out fine material (e.g. small quartz sand, activated carbon particles, etc.) which has been filtered through a variety of media to ensure the quality of the water and to protect the membrane filter element from large particulate matter. Precision filter device installed in the filter element accuracy level can be divided into 0.5us,1us,5us,10us, etc., according to different occasions to choose different filtration accuracy, to ensure the accuracy of the water and ensure the safety of the post-stage membrane elements. The precision filter device is mainly composed of a filter shell, a filter element, etc., and the filter shell is mostly composed of R304 stainless steel material, such as R316 stainless steel for special occasions such as acid and alkali resistance. The filter element in the middle of the filter shell is mainly PP filter cotton core, and wire wound filter or activated carbon filter can also be used in some occasions. The number of filter elements installed can range from one to dozens, mainly according to the size of the processing capacity to determine. picture       Bag filter     Bag filter is a kind of pressure filter device, mainly composed of filter cartridge, filter cartridge cover and quick-opening mechanism, stainless steel filter bag strengthening net and other main components, filtrate by the filter shell side inlet tube into the filter bag, filter bag itself is installed in the strengthening net basket, liquid penetration through the required fineness of the filter bag can obtain qualified filtrate, impurity particles are intercepted by the filter bag. The machine is very convenient to replace the filter bag, filter basically no material consumption.       Bag filter has many advantages such as reasonable structure, good sealing, strong flow ability and easy operation. In particular, the filter bag side leakage probability is small, can correctly ensure the filtration accuracy, and can quickly change the filter bag, so that the operating cost is reduced. The inner and outer surfaces of the filter are solved by mechanical sandblasting, which is average and easy to clean. We know that the filter method taken by the bag filter is the side-in and side-out method, and the method of side-in and side-out can also be taken, and the filter liquid medium is pressed into or pumped into the bag filter barrel through the pressure in the pipeline, and the liquid medium to be filtered is filtered through the electro-polishing punching to support the filter blue filter bag, and the changed solid liquid arrives at the result of the liquid medium being filtered.       The structural design of the bag filter is made of four sets of swinging hammer ring head bolts to seal the top cover and the filter cartridge tightly, so that the filter can withstand extremely high filtration pressure and water hammer pressure impact. The bag filter is composed of three parts: filter drum, filter basket, filter bag, compact structure and simple; The liquid to be filtered enters through the inlet of the filter, flows into the filter bag, and after being intercepted by the filter bag, flows out from the outlet of the filter. The import and export design of bag filter generally adopts the mode of side entry and bottom out, which is convenient for cleaning.

picture 1 Why change the filter?       filter (filter) is an indispensable device on the transmission medium pipeline, usually installed in the pressure reducing valve, pressure relief valve, fixed level valve. The filter has a filter cartridge of a certain size filter screen, and its impurities are blocked, and when it needs to be cleaned, as long as the detachable filter cartridge is removed and re-loaded after treatment.   Daaaaaa!   If the core of the early filter is not cleaned and replaced in time, the ability of the filter to effectively filter harmful substances will be greatly reduced in the early stage, when the output of water exceeds the rating of the effective filter, after the water starts, these substances in the water will not only not be adsorbed, but also be released from the filter to the water. The beginning of this primary filter not only has a lower effect than clean water, but even causes minor pollution.       Basic performance characteristics of the filter:   1. Efficient and accurate filtration: the special structure of the filter disc filtration technology, accurate and sensitive performance, only particles smaller than the required size can enter the system, is an effective filtration system; Specifications are 5μ, 10μ, 20μ, 55μ, 100μ, 130μ, 200μand so on, the system flow can be flexibly adjusted according to needs.   2. Standard modular, saving land: The system is based on the standard disk type filter unit, according to the modular design, users can choose according to demand, flexible and changeable, strong interchangeability. The compact system has a very small footprint and allows flexible installation using corner space.   3. Fully automatic operation, continuous water discharge: between the units in the filter combination, the backwashing process takes turns; Automatic switching between working and backwashing states ensures continuous water discharge; Backwash water consumption is very small, accounting for only 0.5% of the water output; If combined with air assisted backwashing, the water consumption can be reduced to less than 0.2%. High-speed and thorough backwashing takes only tens of seconds to complete.   4. Long life: the new plastic filter element is strong, no wear, no corrosion, very little scaling, after many years of industrial practical verification, the use of 6 to 10 years without wear, no aging, filtration and backwashing effect will not deteriorate due to the use of time.   5. High quality, less maintenance: the products meet the corresponding quality standards, all products are tested and tested by simulated conditions before leaving the factory, no special tools are required, few parts; Easy to use and requires little maintenance.   picture           picture 2 How the filter works     picture The water to be treated by the filter enters the body by the water inlet, and the impurities in the water are deposited on the stainless steel filter screen, resulting in a pressure difference.   Filter outlet pressure difference changes, when the pressure difference reaches the set value, the electric controller gives the hydraulic control valve, drives the motor signal, and causes the following actions: the motor drives the brush to rotate and cleans the filter element; At the same time, the control valve is opened for sewage discharge, the whole cleaning process only lasts for tens of seconds, when the cleaning is finished, the control valve is closed, the motor stops rotating, the system returns to its initial state, and the next filtration process begins. After the equipment is installed, the technical personnel will debug, set the filtration time and cleaning conversion time, the water to be treated enters the body from the water inlet, the filter begins to work normally, when the preset cleaning time is reached, the electric controller gives the hydraulic control valve and drive motor signals, triggering the following actions: The motor drives the brush to rotate, cleaning the filter element, while the control valve is opened for sewage discharge, the whole cleaning process only needs to last tens of seconds, when the cleaning is finished, the control valve is closed, the motor stops rotating, the system returns to its initial state, and begins to enter the next filtration process. The shell of the filter is mainly composed of coarse filter screen, fine filter screen, suction pipe, stainless steel brush or stainless steel nozzle, sealing ring, anti-corrosion coating, rotating shaft and other parts.   picture         picture 3 Product classification of filters     Self-cleaning filter is a kind of precision equipment that uses the filter screen to directly intercept impurities in the water, remove suspended matter and particulate matter in the water body, reduce turbidity, purify water quality, reduce system dirt, bacteria, algae, rust, etc., in order to purify water quality and protect the normal work of other equipment in the system.   The automatic filter is a set of equipment widely used in the filtration industry, which overcomes the shortcomings of traditional filtration products such as small amount of pollution, easy to be blocked by dirt, the filter part needs to be disassembled and cleaned, and the filter status cannot be monitored. It has the function of filtering raw water and automatically cleaning the filter element.   The biggest advantage of the elastic filter is that it is maintenance-free and can be cleaned automatically, avoiding the hidden danger of clogging caused by the long-term work of the filter element. Features: maintenance-free, automatic cleaning, short cleaning time (3 seconds). When cleaning, the spring opening gap is equal and can swing, which can replace the net type, cylinder type, bag type and other filters to reduce the comprehensive cost.   The prototype of the air filter is a respiratory protection device used by people to protect their breathing. It is recorded that as early as the first century in Rome, people used masks made of coarse hemp to protect themselves while purifying mercury. In the long time since then, air filters have also made progress, but they are mainly used as respiratory protection devices in some dangerous industries, such as the production of harmful chemicals. In 1827, Brown discovered the motion law of tiny particles, and people had a further understanding of the mechanism of air filtration.   The liquid filter enables the contaminated liquid to be cleaned to the state required for production and life, that is, to make the liquid reach a certain degree of cleanliness.   Internet filters, which are set up to block spam, make the information on the computer screen as consistent as possible.   The light filter, with the principle of absorption, separates the light of different colors and absorbs some unwanted light.

The main function of the air filter is: air exchange purification, removing the dust particles inside the new gas, which is characterized by low dust concentration in the air, fine particles, and high purification efficiency.   Main frame materials are: paper, aluminum alloy, galvanized steel and so on.   The main filter materials are: glass fiber filter cotton, activated carbon filter cotton, synthetic fiber filter cotton, non-woven filter cotton and so on.   1   Fiberglass filter cotton   Glass fiber filter cotton is mainly made of glass fiber of different thickness and length by special processing technology. Glass fiber with its stable performance, high temperature resistance, high efficiency, large capacity, long service life and so on. And in some special circumstances, only wave lines can do the job. Widely used in the general ventilation system of the initial effect filter, high temperature filter and high efficiency filter, the air filtration requirements of high places and environments.     2   Activated carbon filter cotton   Activated carbon is characterized by the removal of odor in the air. Activated carbon filter cotton refers to synthetic fiber after carbon impregnation and glue treatment. Because the role of activated carbon is to remove odor, there is no emphasis on filtration efficiency. In use. Generally, it must be combined with the use of independent primary and medium efficiency filters.   3   Synthetic fiber filter cotton   In the general filtration environment, it can fully replace non-woven fabrics and glass fiber covering coarse, medium and efficient full series of filtration products, which is an emerging filtration material and the main development direction of filter materials in the future. Compared with other filter materials of the same level, it has the advantages of low resistance, light weight, large capacity, environmental protection (can be incinerated) and moderate price. Use (polyester fibre) as the main raw material, abbreviation abbreviation: PET, polyester fiber is made of polyethylene terephthalate, also known as synthetic fiber or polyester. Polyester has excellent crease resistance, elasticity and dimensional stability, good electrical insulation, sun resistance, friction resistance, no mold and no decay, good chemical agent resistance, weak acid and weak base resistance. The industry name is: chemical fiber, chemical fiber has large chemical fiber and small chemical fiber   4   Non-woven filter cotton   The scientific name polyester fiber, commonly known as non-woven fabric, non-woven fabric has the technical characteristics of wide use, technical maturity, good stability, etc., is the typical filter material of China's current early and medium efficiency plate and bag filter. Compared with other filter materials of the same grade, it has the advantages of stable quality, large dust tolerance, strong moisture resistance, long service life, economic and durable. Non-woven fabrics are also the earliest application of filter materials, mature technology development, low production costs, in recent years due to the continuous progress of technology, the emergence of composite non-woven fabrics greatly improve the image of cheap low-grade non-woven fabrics, in efficiency has been able to achieve sub-efficiency. At the same time, the composite non-woven filter material can also be used for filtration in places with relatively high air cleanliness requirements.

The high-pressure oil suction filter is installed in the oil pump suction port to filter impurities in the oil, to protect the oil pump and other hydraulic components, effectively control the pollution of the hydraulic system, and improve the cleanliness of the hydraulic system.   The filter is equipped with a transmitter, bypass valve, self-sealing valve, and dirt collecting cup. It has the advantages of large oil flow capacity and small resistance. Its main performance features are: 1. The filter can be mounted directly on the side, bottom or upper part of the tank, with the barrel extending into the oil in the tank. The oil outlet is provided with threaded connection and flange connection mode, and is connected with the oil suction port of the oil pump, the pipeline is simple and the installation is convenient. 2. With oil circuit self-sealing device, cleaning filter element is very convenient. When cleaning or replacing the filter element, just unscrew the top cover of the filter, and the self-sealing valve installed at the bottom of the cylinder will close itself, cutting off the oil circuit, so that the oil in the tank will not spill. After assembling the filter element, tighten the upper cover, the self-sealing valve will open by itself, and the filter will enter the working state.   3. The filter element clogging transmitter is provided at the oil outlet of the filter, which has two functions: intuitive and signaling. By observing the transmitter indicator, you can always know the blockage of the filter element, when the filter element is blocked, the oil outlet vacuum degree reaches 0.018MPa, the transmitter will send a signal, at this time should stop cleaning or replacing the filter element. 4. A bypass valve is provided in the upper part of the filter element. When the filter element is blocked by the alarm transmitter, the fault cannot be dealt with immediately. When the vacuum degree of the oil outlet rises to more than 0.032MPa, the bypass valve will open by itself to avoid the suction phenomenon of the oil pump and ensure the normal operation of the hydraulic system. 5. The pollution collecting cup is provided. During the operation of the system, the oil flows through the inner cavity of the filter element, and the filtered pollutants are blocked in the filter element and concentrated in the pollution collecting cup. When the filter element is replaced or cleaned, the pollution collecting cup and the filter element are brought out together to avoid the filtered pollutants falling into the tank again when the filter element is replaced, thus maintaining the cleanliness of the hydraulic oil.

Working medium:   1. It is recommended to choose L-HM46 or similar viscosity hydraulic oil in summer, and L-HM32 or similar viscosity hydraulic oil in winter.   2. Working oil temperature range -20℃~80℃   3. The cleanliness of the system directly affects the reliability of the hydraulic components, before refuting, the oil tank and pipeline should be fully cleaned, the general pump suction side commonly used filter accuracy 100 purpose (its rated flow rate should be not less than twice the pump flow), the oil filter with filtration accuracy of not less than 25μm is connected to the return pipeline.       02   Oil Pump:   1. Before starting the oil pump, carefully check whether the oil inlet and outlet and the rotation direction are consistent with the direction indicated by the sign, and do not reverse rotate.   2. Flexible coupling should be used between the pump transmission shaft and the prime mover output shaft, and the different coaxiality is not greater than 0.1mm.   3. It should be ensured that the pump shaft does not bear radial force, direction force and bending moment. When installing the gear pump, the shaft should be slowly introduced, do not force knock, axial collision, otherwise it will cause serious damage to the pump.   4. The suction height of the pump is not more than 0.5mm.   5. Do not bump on the flange connecting the oil inlet. The joint surface and joint must be strictly sealed to prevent air leakage, otherwise it will cause noise, vibration, foam and other abnormal phenomena, and reduce the life of the gear pump.   6. The diameter of the gear pump suction pipe should ensure that the flow rate of oil is less than 1.5m/s.       03   Oil motor:   1. When installing the motor, the shaft should be slowly imported, do not force it into.   2. Flexible coupling should be used between the motor drive shaft and the power output shaft, and the different coaxiality is not greater than 0.1mm.   3. The back pressure of the motor drain port shall not be greater than 0.4MPa.   4. Carefully check the oil inlet and outlet before the motor is installed, do not reverse rotate, and the direction of the motor rotation should be consistent with the direction indicated by the sign.     04   Hydraulic valve:   1. The joint surface of the valve oil port is strictly prohibited from bumping, ensuring that the joint surface and joint are strictly sealed.   2. When installing the external control mechanism, it should be ensured that the slide valve does not bear lateral force, so that the slide valve movement is flexible and there is no stuck phenomenon.   3. Install each oil port correctly. Do not allow dirt to enter.   4. The rated pressure of the safety valve of the hydraulic power station sold by the company has been adjusted before leaving the factory, and it is strictly prohibited to adjust it at will.       05   Hydraulic cylinder:   1. When the hydraulic cylinder is in the initial movement, the air in the cylinder should be excluded to avoid crawling and abnormal noise. 2. Avoid scratching and bumping the piston rod to avoid seal failure and oil leakage.   3. During installation, attention should be paid to adjusting the piston rod and cylinder coaxial to avoid the piston rod being subjected to lateral force, causing the piston rod to bend and pull the cylinder.   4. The cylinder should check the hydraulic oil before use, and it is strictly prohibited to use harmful or contaminated oil.   5. Check the system pressure before use. It is strictly forbidden to use the oil cylinder over pressure.

The RFB series double barrel direct return oil filter (the new type replaces the SPZU series filter) is composed of two single barrel filters, reversing valve, bypass valve, transmitter, diffuser, etc.   It is installed on the top, side or bottom of the tank, can be replaced in the system without stopping the filter element, suitable for continuous work of the hydraulic system oil fine filtration, used to filter the hydraulic system components wear metal powder and seal rubber impurities, so that the flow of oil back to the tank to keep clean, in order to facilitate the system of oil circulation.   When the filter element of a filter is blocked and the inlet and outlet pressure difference is 0.35MPa, the transmitter sends a signal. At this time, the reversing valve is turned to make the standby oil filter work, and then the blocked filter element is replaced. When the blocked filter element cannot be replaced in time for some reason, so that the pressure difference between the import and export further rises to 0.4MPa, the bypass valve automatically starts to work, so as to protect the filter element and the system to work normally, but the user should replace the filter element as soon as possible. Because there is no check valve, when the filter is placed on the side and bottom of the tank, the oil will not flow out of the tank when changing the filter element. The diffuser is arranged at the bottom of the oil return cylinder, which can make the medium of the oil return flow smoothly into the tank, which is not easy to produce bubbles, reduce the re-entry of air, and weaken the disturbance of the deposited pollutants.

The main function of the hydraulic tank of the excavator is to store the hydraulic oil of the hydraulic system, distribute the heat in the hydraulic oil, and separate the gas and sediment in the hydraulic oil. The hydraulic oil tank is equipped with a partition to prevent excessive fluctuation of hydraulic oil, increase the circulation distance of hydraulic oil, so that the hydraulic oil has enough time to separate bubbles, precipitate impurities, and dissipate heat. The hydraulic oil tank is equipped with an oil suction filter and an oil return filter, which are used to prevent foreign objects such as metal chips generated by hydraulic components from flowing back to the hydraulic system.   picture   1. Oil suction filter structure         The hydraulic oil tank suction filter of medium and large hydraulic excavator is connected with the oil suction port of the main pump, the bottom of which is connected with the flange seat at the bottom of the hydraulic oil tank box, and the top of which is connected with the flange sleeve at the top of the box. The oil suction filter is used to prevent foreign matter in the oil tank from mixing into the main pump and other hydraulic components, and plays a protective role in the main pump and the entire hydraulic system. The oil suction filter is mainly composed of spring 1, large nut 2, connecting rod 3, small nut 4, oil suction filter element 5, etc., as shown in Figure 1.       picture   With the increase of the working time of the excavator, the foreign matter on the oil suction filter element 5 will gradually increase, which can cause the oil absorption resistance to increase. In order to prevent the oil absorbing resistance of the oil absorbing filter element 5 from being too large and to maintain sufficient flow capacity, it is necessary to clean or replace it regularly. Therefore, considering from the structure of the tank box, the oil suction filter element 5 should be convenient to disassemble.           2. Existing problems         There are the following three problems in the installation method of the oil suction filter of the hydraulic tank of the medium and large hydraulic excavator: First, the connecting rod of the oil suction filter is long, and it is difficult to align the installation seat during installation, which is easy to install the phenomenon of not being in place, resulting in the oil suction filter not working normally, and it brings trouble to cleaning and replacing the oil suction filter; Second, there is more oil in the hydraulic oil tank, and the hydraulic oil in the oil tank will shake violently when the excavator is working, which is easy to fall off the oil suction filter and the filter element is broken, resulting in hydraulic oil pollution; Third, due to the large volume of the hydraulic oil tank and the thin steel plate for making the oil tank, the hydraulic oil tank is prone to sucking and bulging after the oil suction filter is blocked.           3. Improvement measures         In view of the above problems of oil suction filter, we designed a new structure of oil suction filter which is easy to fix for the hydraulic tank of medium and large hydraulic excavator.       (1) Technical solutions   The improved hydraulic oil tank is composed of flange cover 1, partition board 2, fixing plate 3, oil suction filter 4, cleaning hole flange 5, mounting seat 6, connecting rod 7 and box, etc., as shown in Figure 2. The partition board 2 and the fixed plate 3 are welded to the inside of the box; The flange cover 1 is welded with a sleeve, and the fixing plate 3 is welded with a guide seat; The center of the mounting seat 6, flange cover 1 and guide seat at the bottom of the tank is a vertical center line. A cleaning hole is made on the oil tank box at the corresponding part of the oil suction filter 4, and a cleaning hole flange 5 is installed on the cleaning hole.   picture   (2) Installation method   The oil suction filter 4 is fixed by the sleeve on the mounting seat 6, the fixing plate 3 and the flange cover 1. The installation method is as follows: First, put the oil suction filter 4 with connecting rod 7 into the hydraulic oil tank from the flange cover 1, and place it on the mounting seat through the guide seat on the fixing plate 3; Secondly, the position of the oil absorption filter 4 is corrected, and the oil absorption filter 4 is positioned on the mounting seat 6; Finally, observe the oil suction filter 4 at the cleaning hole flange 5, install the flange cover 1, and fix the oil suction filter 4 through the sleeve and connecting rod 7 on the flange cover 1. The 3D view inside the hydraulic tank with the oil filter installed is shown in Figure 3.       picture           Step 4: Features     The improved hydraulic oil tank has the following four characteristics: First, the diaphragm and the fixed plate divide the hydraulic oil tank into three smaller cavities, and the volume of each cavity is smaller, which reduces the shaking of hydraulic oil in the box, reduces the impact of hydraulic oil on the oil suction filter, and increases the structural strength of the hydraulic oil tank box; Second, the fixed plate and the mounting seat fix the oil filter in the box to effectively prevent the oil filter from falling off; Third, the guide seat on the fixed plate plays a guiding role in the installation of the oil suction filter, which is easy to install the oil suction filter; Fourth, the cleaning hole flange 5 is added to facilitate the cleaning and replacement of the oil filter element.

1 The role of the filter in the hydraulic system   The role of the filter in the hydraulic system is:   1) Filter the dirt particles in the oil, prevent the moving parts from jamming, parts scratches, oil passage blockage and other failures, and improve the reliability and stability of the system.   2) Filter out fine particles of impurities in the oil, prevent abrasive wear of parts, and extend service life. For this reason, the filtration accuracy should meet the sliding clearance that needs to be protected.   3) By analyzing the accumulated pollutants in the filter, analyzing the hidden trouble, finding the worn parts, and monitoring the operation of the equipment.   2 Filter type   The filter used in the hydraulic system is divided into three types, namely surface type, depth type and adsorption type, according to the filtration mechanism of the filter material.   1) Surface type filter   Filtering is achieved by a geometric surface.   The filter element material has a uniform calibration hole, which can filter out particles larger than the size of the hole. The filtered particles are trapped on the surface of the filter element on the upstream side of the oil.   Because the particles gather on the surface, the filter element is easily blocked and needs to be cleaned regularly.   Mesh filters and wire gap filters belong to this category.   The filter element is composed of copper wire mesh wrapped on the core frame. The filtration accuracy is low, which is related to the mesh size and the number of mesh layers. There are 80, 100, 180μm. For pressure pipeline, commonly used 100, 150, 200 copper wire mesh; For hydraulic pump suction pipe, commonly used 20 ~ 40 copper wire mesh. Pressure loss does not exceed 0.004MPa. Simple structure, large circulation capacity, convenient cleaning.   The filter element is composed of metal wire wound on the core frame, and the small gap between the lines is used to block the passage of particles. High filtration accuracy, 30, 50, 80μm and other three grades. For low pressure lines. Pressure loss does not exceed 0.03 ~ 0.06MPa. The structure is simple, the flow capacity is large, the strength of the filter material is low, and it is not easy to clean.   2) Depth filter   The filter element is composed of porous permeable material and has a zigzag channel inside. Particles larger than the surface aperture are trapped on the outer surface; Smaller particles enter the material and are adsorbed by the channel wall. Paper, felt, sintered metal, ceramics, various fiber products and other filter elements of the filter belongs to this category.   ① Paper core filter. The structure is the same as the line-gap filter, but the filter element is made of plain and corrugated chemical fiber or wood pulp microporous filter paper. In order to increase the filtering area, the paper core is often made into a folded shape. In order to enhance the strength of the filter element, its inner and outer sides are usually reinforced with metal mesh. High filtration accuracy, up to 5 ~ 20μm. The pressure loss is about 0.01 ~ 0.4MPa.   ② sintered filter. The filter element is sintered from metal powder, and micropores between metal particles are used to block the particles in the oil. The filtration accuracy is high, up to 5 ~ 10 μm, and the filtration accuracy can be changed by changing the size of the metal powder particles. Suitable for fine filtration.   3) Adsorption filter   The filter material adsorbs the particles in the oil onto the filter. Magnetic filters are adsorption filters, made of permanent magnets, which can absorb iron filings, iron powder or magnetic abrasives in the oil. It is usually combined with other types of filters to make a compound filter. Magnetic filters also monitor the wear of mechanical equipment.   Magnetic filter is divided into ordinary magnetic filter and high gradient magnetic filter. Ordinary magnetic filters use the magnetic field of the magnet to directly capture ferromagnetic pollution particles in the oil. Among them, the permanent magnet filter has the advantages of simple structure, convenient manufacturing, reliable operation and low operating cost, so it is widely used, and its main disadvantages are poor particle capture effect, and the particles adsorbed on the magnetic pole are difficult to clean. The high gradient magnetic filter can effectively overcome the above shortcomings, so that the performance of the magnetic filter is greatly improved.   The attraction of ferromagnetic particles is proportional to the external magnetic field intensity H, and is proportional to the gradient gradH of the magnetic field intensity.   Ordinary magnetic filter is to improve the magnetic attraction by increasing the external magnetic field strength H, so as to improve the filtration capacity; The high gradient magnetic filter is to increase the attraction by increasing the gradient gradH of the magnetic field through the magnetic medium to obtain the effect of efficient filtering of pollutants.   The arrangement of polymagnetic porous media in the magnetic field will make the magnetic field H and magnetic gradient gradH near the magnetic medium much larger than that without magnetic medium, especially gradH is inversely proportional to the magnetic medium section diameter d, when d is very small, the gradH value can be very high. Therefore, the high gradient magnetic filter based on this principle is also called the high efficiency magnetic filter.   The high gradient magnetic filter uses the magnetic medium magnetized by the magnet to capture the pollution particles, and the magnetic medium can greatly improve the magnetic field gradient around the medium, so the filtration performance of the high gradient magnetic filter is significantly higher than that of the traditional magnetic filter.

Pressure switch characteristic   Understanding system dynamics is essential for switch selection. Here is a list of questions to answer when specifying the pressure switch:       How often is the switch activated? Electromechanical switches are prone to fatigue. Bourdon tube or diaphragm switches typically provide 1 million cycles compared to piston or diaphragm sealed piston switches that provide 2 million cycles. Since the solid-state switch does not get tired, it typically runs 100 million cycles. Exceptions may occur when the pressure change in the system is small, 20% or less of the adjustable range. In this case, a Bourdon tube or diaphragm switch can be used for up to 2 million cycles before fatigue.   picture       What's the cycle speed? Bourdon tube or diaphragm switch metal analog springs, so high-speed cycling should be avoided. When the cycle rate is below 25/min, Bourdon tube or diaphragm switch is a good choice. For cycle rates of 25 to 50 cycles per minute, piston or diaphragm sealed piston switches typically provide 2 million cycles. When the cycle rate exceeds 50 cycles/min, a solid-state switch should be selected because fatigue is not a problem.       How does the switching point relate to the operating pressure range? The relationship between choosing the right switch point and the operating pressure range of the switch affects accuracy and life. The general rules for solid-state switches and electromechanical switches are different. For solid-state switches, the switching point should normally be at the upper 25% of the operating range. For electromechanical switches, the switching point should be in the middle of the working range. Systems that require a switch to start at 140 psi should use a solid state pressure switch with an operating range of 150 psi, or an electromechanical switch with an operating range of 300 psi. Exceptions should be made when the system experiences violent pressure fluctuations or when life or accuracy is the most important issue.       High pressure spikes and surges Pressure surges and transient pressure spikes can greatly exceed the normal operating pressure of the system. It is not uncommon for the switch to fail because the peak pressure exceeds the validation pressure, which is the maximum pressure the switch can withstand without damage. Bourdon tubes, diaphragms and solid state pressure switches are sensitive to surges and spikes. If the system is expected to be affected by surges, choose a switch with a higher voltage withstand or install a buffer to dissipate spikes without damaging the switch.       How many switch points are needed? When pressure is induced at a certain point, usually only one switching point is needed. However, some systems require two or even four switch points to monitor, control, or alarm. When designing the system, choose a switch for each switch point, or a pressure switch capable of handling up to six separate switch points. Most sensors use a duplex switch, and a few have a built-in three-switch function. Solid-state switches can have up to six or more independent switching points.       Switch housing Bare wire switches have no housing. They are usually mounted in a panel or multifunctional housing. The closed switch can avoid the danger caused by loose wires in the exposed position. They are typically available in a variety of ratings, with the most widely used industrial switch housings being NEMA 4 and NEMA 4X for aggressive environments. Terminal pressure switch installed and equipped with closed terminal. This eliminates the cost of purchasing and installing external junction boxes. The housing of the explosion-proof pressure switch is designed to meet recognized electrical standards to isolate equipment from hazardous environments.       Set point adjustment In some applications, set points are permanently fixed, while in others some adjustments are required. Electromechanical switches with factory Settings, coarse adjustment capabilities, or models provided with calibration adjustment knobs. Solid-state switches provide precise keyboard adjustments via digital readings.       Need a tight dead zone or a wide dead zone? The dead zone or drive value of the switch can be adjusted at the factory setting or at a certain percentage of the entire pressure range. Traditionally, security services have used narrow dead zones. Wider dead zones are used in control circuits such as hydraulics. Tight or narrow dead zones often appear on bourdon tubes and diaphragm switches; Piston switches provide a wide dead zone; Solid state switches offer close to 100% full scale dead zones.       Some of the information on diaphragm and Bourdon tube pressure switches was adapted from information published by Delaval's Barksdale Division.   There are several types of pressure switches to choose from. The designer should choose a type that can be expected to give the most satisfactory results for his type of application.   Basic type At low pressure (compressed air and extremely low pressure hydraulic systems), diaphragm and bellows movements are most often used, and sometimes Bourdon tube movements. At high pressures, piston and bourdon tube movements are most common. With the exception of switches with tilted mercury contacts driven by Bourdon tubes, quick-acting contacts appear to be commonly used.   Expected service life The expected service life is usually limited by the type of pressure sensing mechanism - Bourdon tube, diaphragm, piston, dish spring, etc. It is assumed that the quick-acting contact has a longer service life than the sensing mechanism.   If the service life (the number of cycles expected for switch operation) is less than one million, it indicates a Bourdon tube or diaphragm type. If there are more than a million cycles, the piston type should be used. An exception to this rule is when the pressure in the system changes very little (20% or less of the adjustable range). In this case, Bourdon tube or diaphragm switches can be used for up to 2.5 million cycles before metal fatigue or contact failure.   Riding speed In addition to service life, riding speed must also be considered. If the switch is expected to cycle more than once every 3 seconds, the piston switch should be specified. The metal of any Bourdon tube or diaphragm switch acts as a spring, which heats up and tires during extremely fast cycle operation, thereby shortening the service life of the switch.   precision Diaphragm and Bourdon tube pressure switches generally have higher accuracy than piston switches, and in cases where accuracy is important, they will be preferred if they meet service life and cycle speed requirements.   A switch with a dish spring (quick action) seems to offer the greatest repeatability, but the manufacturer should be contacted for the life expectancy of the spring.   picture       Figure 1. On the switch with diaphragm and Bourdon tube movement, the highest accuracy is 65% above, The optimal life factor is in the lower 65%, and the optimal combination is usually in the middle 30% of its operating range (zone A).       Adjustable range The term "operating range" defines the range of pressures that a switch may see under normal operating conditions. This is usually an adjustable range.   For maximum accuracy, the set point should fall within the upper 65% of the adjustable range. But for the most favorable life factor, the set point should be in the lower 65% of the adjustable range. Therefore, the optimal combination of accuracy and life coefficient is located in the middle 30% of the adjustable range, as shown in the figure. This general rule applies to diaphragm and Bourdon tube pressure switches. The piston switch has closer to consistent accuracy and life coefficient in its adjustable range.   Type of switch action   Standard pressure switches sense a single pressure source and open or close a set of contacts.   The differential pressure switch has two connections that can sense the differential pressure of the entire circuit.   The double switch senses the upper and lower limits of the same pressure source and activates two sets of electrical contacts. A wide range of dual pressure sensing can be achieved using two standard pressure switches. See the picture below.   Fluid medium The compatibility of the fluid with the structural material must be considered. Consult the switch manufacturer directory.   Withstand voltage Voltage resistance is the highest pressure that a switch can withstand without permanent deformation, usually defined as 1.5 times the maximum operating range. Although the pressure gauge in the system may show a constant operating pressure, surges suppressed by holes in the gauge may occur, which can damage the diaphragm and bourdon tube elements in the pressure switch. Therefore, the working range should be much higher than the actual working point.       picture       Figure 2. Infinite difference between cut and cut pressure.       wide Differential pressure sensing While some pressure switches can regulate differential pressure (the difference in pressure required to open and close switch contacts), this differential pressure may not be wide enough for some applications.   The circuit in Figure 2 can be adjusted for almost infinite switching differences. It uses two standard pressure switches and a hold relay.   One pressure switch is used for the high pressure cut-off point and the other pressure switch is used for the low pressure cut-off point. The relay CR has a set of normally open holding contacts CR1 and a set of load switching contacts CR2, which can be normally open or normally closed according to circuit requirements. The circuit acts as follows: starting from zero system pressure, with the pressure, as the pressure rises, the "low" pressure switch will close, but this has no effect on the switching circuit. As the pressure rises further, the "high" pressure switch will close. "The pressure switch will close and the coil of the relay CR will be energized. The relay is electrically locked by contact CR1 and "low" pressure switch. Relay contact CR2 will disconnect the switching circuit. As the pressure drops, the "high" switch will disconnect, but this has no effect on the switching circuit. As the pressure drops further, the "low" switch will open, unlocking the hold relay. Contact CR2 closes the switching circuit.

Float flowmeters include metal tube float flowmeters and glass float flowmeters (glass rotor flowmeters). Generally speaking, the float flowmeter is suitable for small pipe diameter and low flow rate working environment, commonly used instrument diameter is below 40-50mm, the minimum diameter is 1.5-4mm. Taking liquid as an example, the nominal pipe diameter of the full degree flow of the glass tube float flowmeter with a diameter below 10mm has a flow rate of only 0.2-0.6m/s, or even lower than 0.1m/s; The metal tube float flowmeter and the glass tube float flowmeter with a diameter greater than 15mm are slightly higher, and the flow rate is between 0.5-1.5m/s. Float flowmeter can be used for lower Reynolds number, the choice of viscosity insensitive shape of the float, the Reynolds number at the flow ring gap is greater than 40 or 500, the Reynolds number change flow coefficient is maintained constant, that is, the fluid viscosity change does not affect the flow coefficient, the value is far lower than the standard orifice plate and other throttled differential pressure flow meter minimum Reynolds number 104-105 requirements.   In actual use, float flowmeters often need to be used with magnetic filters. Magnetic filter is mainly suitable for separating the function of the liquid medium containing fine iron debris, so that it can meet the process requirements required by the liquid medium, so it is widely used in the food industry, medicine, cosmetics, fine chemicals and other industries, at the same time, the double filter drum magnetic filter is equipped with two reversing valve composition, a group of filter device is put into operation when cleaning, change the reversing valve position, The other group can run continuously to change the position of the reversing valve when cleaning, and the other group can run continuously to ensure the continuity of the process pipeline.   picture The magnetic filter is composed of a strong magnetic material with high coercivity and a blocking filter, and the adsorption force is ten times that of the general magnetic material. It has the ability to adsorb micron level ferromagnetic pollutants in the state of instantaneous flow impact or high flow rate. And it can overcome the ferromagnetic pollutants rushed down under the high-speed impact to be adsorbed again, so as to avoid the hydraulic components stuck or friction pay wear, extend the service life of the hydraulic components and hydraulic system, and enhance the reliability of the hydraulic system. Its center is a cylindrical permanent magnet, the outside of the magnet is made of non-magnetic material cover, cover around a number of iron rings, iron rings are connected by copper strips, and each iron ring maintains a certain gap. When the ferromagnetic impurities in the hydraulic medium pass through the iron ring gap, they are adsorbed on the iron ring, so as to play a filter role. In order to facilitate cleaning, the iron ring is divided into two halves, when the impurities will block the gap, the iron ring can be removed and cleaned, and then installed and used repeatedly.   Magnetic filter Magnetic filter can also be combined with other filter materials to form a composite filter for paper filter filter on the oil return circuit. The filter paper filter element is made of an inner cylinder, an outer cylinder and an oil filter paper sandwiched in the middle. The inner and outer cylinder is rolled by thin steel plate, and there are many round holes through oil on the plate; The filter paper is folded into a star shape to increase the flow area. The central pull rod of the filter element is equipped with a magnetic filter element composed of many magnetic rings and nylon spacers. The hydraulic medium that needs to be filtered is first magnetically filtered, and then filtered from the inside out through the paper filter. When the filter element is seriously blocked, the filter inlet pressure rises, so the spring is compressed, the filter element is moved down, and the oil passes directly through the tank between the filter element and the seat to protect the filter element from being crushed.