Imported valves mainly refer to valves from foreign brands, mainly European and American brands. The more representative brands are British Spirax Sarco, German Lite LIT, Japan Kitazawa KITZ, American Ritz RETZ, etc. The product types mainly include imported ball valves, imported shut-off valves, imported regulating valves, imported butterfly valves, imported pressure reducing valves, imported solenoid valves, etc., and the product has many parameters such as caliber, pressure, temperature, material, connection method and operation mode. It is necessary to select the appropriate valve according to the actual needs and characteristics of the product; this paper combines the German brand German Lite LIT, which has been well received by a wide range of customers, to analyze the specific selection of the imported valve: 1. The characteristics of the imported valve have the use characteristics and structural characteristics. The use characteristics of the imported valve determine the main performance and scope of use of the valve. The characteristics of the valve are: the type of valve (closed valve, regulating valve, safety valve, etc.); product type (gate valve, globe valve, butterfly valve, Ball valve, etc.; main parts of the valve (valve body, valve cover, valve stem, valve disc, sealing surface) Material; valve drive methods. 2, structural characteristics Structural characteristics determine the structural characteristics of the valve installation, maintenance, maintenance and other methods, belonging to the structural characteristics are: the structural length of the valve and the overall height, the connection with the pipe (flange connection, threaded connection, clamp Hoop connection, external thread connection, welding end connection, etc.); form of sealing surface (insert ring, thread ring, surfacing, spray welding, valve body); valve stem structure (rotating rod, lifting rod). Second, the choice of valve steps to determine the use of the valve in the equipment or equipment, determine the working conditions of the valve: applicable medium, working pressure, working temperature, etc.; for example, want to choose a German Lite LIT shut-off valve, confirm the medium It is steam, working principle is 1.3Mpa, working temperature is 200 °C. Determine the nominal diameter and connection method of the pipe connected to the valve: flange, thread, welding, etc.; for example, select the inlet shut-off valve and confirm that the connection method is flanged. Determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electro-hydraulic linkage, etc.; for example, the manual shut-off valve is selected. Determine the material of the casing and internal parts of the selected valve according to the medium, working pressure and working temperature delivered by the pipeline: cast steel, carbon steel, stainless steel, alloy steel, stainless acid-resistant steel, gray cast iron, malleable cast iron, ductile iron, copper Alloys, etc.; such as cast steel material selected by the stop valve. Select the type of valve: closed-circuit valve, regulating valve, safety valve, etc.; determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.; determine the parameters of the valve: For automatic valves, determine the allowable flow resistance, discharge capacity, back pressure, etc. according to different needs, and then determine the nominal diameter of the pipe and the diameter of the seat hole; determine the geometric parameters of the selected valve: structural length, flange connection and Dimensions, dimensions of the height direction of the valve after opening and closing, size and number of bolt holes to be connected, dimensions of the entire valve, etc.; use existing information: valve catalogue, valve product samples, etc. to select the appropriate valve product. Third, select the valve according to the purpose of the selected valve, the use of working conditions and control methods; The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable, easy Explosive medium, viscosity of medium, etc.; for example, if you want to choose the imported solenoid valve of German Lite LIT, the medium and environment are flammable and explosive, generally choose the explosion-proof solenoid valve; for example, choose the ball valve of German Lite LIT, the medium contains solid For pellets, a V-shaped hard seal ball valve is generally selected. Requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing grade, etc.; Installation dimensions and dimensions: nominal diameter, connection to piping, connection size, external dimensions or weight restrictions; Additional requirements for reliability, service life and explosion-proof performance of electric units (note that when selecting parameters: if the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, normal flow Pressure drop, pressure drop at closing, maximum and minimum inlet pressure of the valve). According to the above-mentioned basis and steps of selecting the valve, the internal structure of each type of valve must be well understood in order to properly and correctly select the valve, so that the correct choice can be made for the preferred valve. The final control of the pipe is the valve. The valve opening and closing member controls the flow direction of the medium in the pipe. The shape of the valve flow path allows the valve to have a certain flow characteristic, which must be taken into account when selecting the valve suitable for installation of the pipe system. In summary, select several major factors: determine the valve to be used, confirm the temperature and pressure of the medium, confirm the flow of the valve and the required diameter, and confirm the material and operation mode of the valve;