Abstract: Hydraulic fluid power transmission is the hot area of ​​research, the filter in the hydraulic system is very important auxiliary components. The smaller the viscosity of water, water pressure must be controlled with the surface components Keywords: filters; hydraulic transmission; corrosion; seal; filtration

According to the system pressure and flow characteristics of the pipeline, the filter installed in different locations, the structure type and filter selection is also different. Hydraulic system filters the water main pipe installed in the pump, pressure pipes and low pressure pipeline. Because these three pipeline pressure and flow of different sizes, the choice of filters should also be considered separately.
3 Conclusion
Pressure transmission medium due to the special nature of the work, the structure of components and materials used have higher requirements. As an important auxiliary system components, design, processing, filter installation must be considered when the material corrosion resistance, mechanical strength, abrasion resistance, and to choose adequate filtration and filtration capacity of filter. A key technology for hydraulic transmission
Hydraulic drive with water as the working medium. Compared with mineral oil, water has low viscosity, corrosion resistance, compressibility is small, thermal expansion coefficient, heat capacity and thermal conductivity and other properties, while the lower viscosity of water, restricting the water highly corrosive pressure transmission bottleneck technology development 2.
1.1 Sealing Technology
Hydraulic components of the gap between the spool and valve body, leakage of hydraulic transmission gap is mainly leakage. Concentric ring cracks due to pressure difference generated by leakage, for example, the leakage rate calculation formula is:

One: Q for the leakage / (m. · S-1); as the gap volume / m; of hole diameter / m; △ poor households for the gap at both ends of the pressure / Pa; the gap length / m; is the dynamic viscosity / ( Pa · s).
Where, QoC 1 / L, QoC. Only due to water viscosity mineral oil 1/12o ~ 1 / 30 [deputy, apparently, in the same pressure, the gap structure size is also under the same conditions, the leakage of hydraulic transmission, compared with the amount of leakage of hydraulic 3O ~ 120 times the efficiency of the system greatly reduced. As a pressure transmission system, one way to reduce leakage as much as possible the amount of control the gap, this requirement is to enhance the dimensional accuracy with the surface, reducing the gap is, of course, with the pieces to ensure that the relative movement needs. However, with the gap decreases, the water pollution will therefore plug the gap, resulting in failure of the action of moving parts, and even stuck, causing system failure. Practice has proved that, due to fluid power systems around the work of media failure 8O pollution. Thus, the development of pressure transmission to adapt the filter is particularly important.
2 hydraulic transmission filter
Hydraulic system filters role is to remove the impurities mixed with water to reduce water pollution and ensure the system works.
2.1 Filter performance
(1) filtration shall meet the requirements of hydraulic systems. Filtration, also known as absolute filtration accuracy, refers to the fluid through the filter, contaminants can pass through the filter of the maximum diameter spherical d / ~ m (ie the maximum orifice size of the filter medium value). Natural water contains large amounts of solid impurities, there are microorganisms, such as sea water barnacles, algae, bacteria, viruses and protoplasm and so on. Some of them with a hard shell, small and irregular shape, most likely through the filter into the system. In addition to the system invaders, there will be some of the resultant systems, such as corrosion of the strip material components, moving parts due to friction, wear metal particles generated. Select the filter accuracy, you should consider the following: particle size of impurities should be less than the surface component movement gap (the gap should be half of normal) or the water film thickness, in order to avoid impurity particles stuck to moving parts or sharp parts that wear; also called the particle size is less than the system of impurities orifice or gap of minimum clearance, so as to avoid congestion; In addition, the higher the system pressure, sliding clearance requirements of smaller components, the higher the filtration accuracy. According to the characteristics of hydraulic systems, general requirements for d <~ 10m, usually used precision (5 ~ 10 m), and even special fine (<5 m) filter.
(2) has a sufficiently large filter capacity, pressure loss. Filtering capacity is under a certain pressure to allow maximum flow through the filter. The ability of filters required, should be combined with the filter is installed in the system to consider, if installed in the suction pipe on the road, its ability to filter the pump flow should be more than 2 times. Flow of water through the filter, will produce pressure loss, the size of the water flow, viscosity and mixed with impurities in the water quantity. In order to maintain the filter does not damage or loss of system pressure will not be too large to limit the maximum allowable filter pressure drop. The filter's maximum allowable pressure drop depends on the strength of the filter. Usually requires pressure drop control 0.03 ~ O. About 07 MPa.
Of the filter depends on the effective filtration area of ​​filter, the performance of the filter itself, the viscosity of water, filter pressure and water content of solid particles. Filter pressure drop the greater the resistance the more hours, the greater the filter's filtering capabilities. Water flow rate through the filter of the lower surface of the pressure the smaller the higher the filtration accuracy. Filter design based mainly on work pressure and filtration requirements of selected filter materials, according to the required flow and choice of filter material to calculate the filter area. Effective filter area filter

Of which: Q is a filter rated flow / (L · min); for the dynamic viscosity of water / (Pa · s); Ap is pressure difference / Pa; a filter material for the filtration capacity of the unit / (L · cm) by experimental determination.
(3) should have good corrosion resistance. Shell and the filter material should have sufficient corrosion resistance. Shell-like materials have a good selection of stainless steel corrosion resistance, but also use other light metal material, while the metal surface coated anti-corrosion coating. Anti-corrosion coatings, epoxy paint is easier to forming, curing performance, good mechanical properties, especially the strong adhesion of metals, alkali resistance is very good, you can use. The stainless steel and epoxy powder coating methods to achieve optimal combination through the polarization generated powder epoxy coating, better wear resistance. Filter can be used bronze powder metal powder pressing, high strength, shock resistance to withstand thermal stress and good corrosion resistance ability to create simple. But it is easy to plug and difficult to clean. Made of stainless steel fiber filter, corrosion resistant, high filtration precision and easy to clean. The liquid can be applied to inorganic fiber made of synthetic resin impregnated resin filter, intensity, filtering and high precision.
(4) cleaning and easy maintenance, easy filter replacement. The higher accuracy of the filter, filter clogging sooner, filter cleaning or replacement cycle shorter. Therefore, the structural design as simple as possible seasonal, compact, fully taking into account the ease of maintenance. Low cost as possible.
(5) filter and the shell has sufficient mechanical strength to withstand high impact.
(6) within the specified operating temperature, can be stable, have adequate durability.
2.2 Use of filters
According to the system pressure and flow characteristics of the pipeline, the filter installed in different locations, the structure type and filter selection is also different. Hydraulic system filters the water main pipe installed in the pump, pressure pipes and low pressure pipeline. Because these three pipeline pressure and flow of different sizes, the choice of filters should also be considered separately.
(1) installed in the suction pipe on the road. To ensure the normal operation of the pump, suction pipes have a vacuum. Filter requires a strong ability to filter and pump flow rate of more than two times; pressure loss is smaller, usually no more than 0.03 MPa; immersed in a water tank installed under the surface, to prevent air intrusion system. Generally used in lower surface filtration type filters using comb filter or line-gap-type corrosion.
(2) install a pressure on the road, protect the system components. Filter and housing requirements and strong anti-corrosion materials, high pressure, sufficient mechanical strength, high filtration precision, can have a larger pressure loss. After installation of the relief valve, or parallel with the safety valve, but the safety valve opening pressure should be slightly lower than the maximum allowable pressure filter. Generally used in depth-type filter, stainless steel fiber or synthetic resin filter, filtering and high precision.
(3) low-pressure pipe installed in the road, back to the main tank to ensure cleanliness of the working medium. Filter can be used with the general accuracy of the low-pressure filter. Only one way to use filters, can not be installed in the flow direction of the constantly changing pipeline. If you must set the filter during this line should be used in conjunction with one-way valve.
3 Conclusion
Pressure transmission medium due to the special nature of the work, the structure of components and materials used have higher requirements. As an important auxiliary system components, design, processing, filter installation must be considered when the material corrosion resistance, mechanical strength, abrasion resistance, and to choose adequate filtration and filtration capacity of filter.