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Abstract: This lecture focuses on summarizing and analyzing the key considerations for the proper selection of control valves. It outlines the experience and precautions related to valve selection based on nine aspects: valve type, actuator, material, flow characteristics, operation mode, spring range, flow direction, packing, and accessories. Selection of valve type: (1) Determine the nominal pressure; instead of using Pmax to determine PN, the appropriate PN is found from a table based on temperature, pressure, and material specifications, ensuring that it meets the PN requirement of the selected valve. (2) The selected valve type has a leakage rate that meets the process requirements. (3) For the selected valve type, its operating pressure difference should be less than the allowable pressure difference of the valve; if this is not possible, special considerations must be given or another valve should be chosen. (4) The temperature of the medium is within the operating temperature range of the valve, and the ambient temperature meets the requirements. (5) Consider the issue of valve clogging based on the cleanliness of the medium. (6) Consider the corrosion resistance of the valve based on the chemical properties of the medium. (7) Consider the erosion and wear resistance of the valve based on the pressure difference and the medium containing hard particles. (8) Performance-to-price ratio considering comprehensive economic effects. Three issues need to be considered: a. Simple structure (the simpler, the higher the reliability), easy maintenance, and availability of spare parts ； b. Service life ； c. Price. (9) Preferred order. Butterfly valve – Single-seat valve – Double-seat valve – Sleeve valve – Angle valve – Three-way valve – Ball valve – Eccentric rotary valve – Diaphragm valve. Selection of actuator: (1) The simplest is the pneumatic diaphragm type, followed by the piston type, and finally the electric type. (2) The main advantage of electric actuators is the convenience of the power source, but they are expensive, and their reliability as well as their resistance to water and explosions are inferior to those of pneumatic actuators; therefore, pneumatic actuators should be given priority. (3) Old electric actuators are bulky; we offer electronic, compact, and highly reliable electric actuators (at a correspondingly higher price). (4) The old ZMA and ZMB film actuators can be phased out, to be replaced by multi-spring lightweight actuators (with improved performance and a weight and height reduction of about 30%). (5) There are many varieties and specifications of piston actuators; older, large, and bulky types are not recommended anymore, and lighter, newer designs should be chosen instead. Material selection: (1) The pressure rating, operating temperature, and corrosion resistance of the valve body should meet or exceed the requirements of the process connection pipes, and preferrably, products that are standardized by the manufacturer should be chosen. (2) Cast iron valves are not suitable for water vapor or humid gases with high moisture content, as well as flammable and explosive substances. (3) When the ambient temperature is below –20°C (especially in the north), cast iron valves are not suitable. (4) In the rectangular coordinate system defined by medium temperature and pressure difference, where cavitation and erosion are severe, areas outside the line connecting the points of 300°C temperature and 1.5 MPa pressure difference require the use of wear-resistant materials for the throttle sealing surfaces, such as cobalt-based alloys or Stellite alloys deposited on the surface. (5) For highly corrosive media, when selecting corrosion-resistant alloys, it is necessary to choose appropriate materials based on the type, concentration, temperature, and pressure of the medium. (6) The valve body and the throttling element are treated separately; the inner wall of the valve body experiences a low throttling velocity and can tolerate a certain degree of corrosion, with an erosion rate of around 1 mm per year ； The throttle element is subject to high-speed erosion and corrosion, which can lead to increased leakage; its corrosion rate should be less than 0.1 mm per year. (7) When selecting the lining material (rubber, plastic), the temperature, pressure, and concentration of the working medium must all fall within the range suitable for that material; At the same time, consideration must be given to the physical and mechanical damage that may occur to it during valve operation (such as shear failure). (8) For vacuum valves, it is not advisable to use a valve body with a rubber or plastic lining. (9) Rubber-lined materials should not be used for the two-position cut-off valves in water treatment systems. (10) Selection of typical corrosion-resistant alloy materials for typical media: a. Sulfuric acid: 316L, Hastelloy, Alloy 20. b. Nitric acid: aluminum, C4 steel, C6 steel. c. Hydrochloric acid: Haas B. d. Hydrofluoric acid: Monel. e. Acetic acid, formic acid: 316L, Hastelloy. f. Phosphoric acid: for nickel alloys and Hastelloy. g. Urea: 316L. h. Caustic soda: Monel. i. Chlorine: Hastelloy C. j. Seawater: Inconel, 316L. (11) To date, the most versatile corrosion-resistant material is tetrafluoro, known as the \"king of corrosion resistance\". Therefore, tetrafluoro corrosion-resistant valves should be chosen first; alloys should only be used as a last resort (e.g., when the temperature is >180°C and PN > 1.6). Selection of flow characteristic: The options provided below are preliminary; for detailed choices, refer to the specialized documentation: (1) Choose logarithmic characteristic when S > 0.6. (2) Choose logarithmic characteristic for operation at low opening degrees and when the unbalanced force varies greatly. (3) Choose when the required adjusted parameter has a fast response speed