1, valve type selection: (1) determine the nominal pressure, not to cover with PMAX PN, but by the temperature, pressure, material from the table to find the three conditions of the corresponding PN and PN to meet the value of the selected valve. (2) to determine the valve type, the leakage to meet the process requirements. (3) to determine the valve type, the working pressure should be less than the valve to allow pressure, such as not, shall be elected from a special point of view or its valve. (4) medium temperature in the valve's operating temperature range, ambient temperature to meet the requirements. (5) According to the media considered not clean the valve attempts to prevent the problem. (6) According to the media to consider the chemical properties of corrosion resistant valves. (7) According to media pressure and with a hard object, consider the valve problems of erosion and abrasion. (8) consider the overall economic effect of performance and price ratio. Need to consider three questions: A, structure is simple (as simple as higher reliability), easy maintenance, a source of spare parts; B, life; C, price. (9) preferred order. Butterfly - Single-seat valve - valve seat - sleeve valve - angle valve - three way valve - Ball Valve - Eccentric rotary valve - diaphragm valve. 2, the choice of implementing agencies: (1) The simplest is the pneumatic membrane, followed by the piston, and finally electric. (2) The main advantage of electric actuators is the driving source (power) to facilitate, but the price is high, reliability, water proof as pneumatic actuators, pneumatic it should be preferred. (3) old heavy electric actuator, we have electronic high-precision small to provide reliable electric actuator (price correspondingly high.) (4) old ZMA, ZMB film actuator can be eliminated by the implementing agency on behalf of many of the spring light (performance improvement, weight, height decreased by about 30%). (5) piston actuator specification more variety, the old, big, stupid advice is no longer used, and use the new structure of light. 3, the choice of materials: (1) valve pressure rating, temperature and corrosion resistance, etc. should not be less than the requirements of the pipeline process connections, and factory approved products should be preferred. (2) Water vapor or water more wet gas and explosive media, should not use cast iron valve. (3) when the ambient temperature is below -20 ℃ (especially the north), should not use cast iron valve. (4) cavitation, erosion and more severe temperature and pressure medium consisting of rectangular coordinates, the temperature is 300 ℃, pressure outside the connection points for the 1.5MPA areas, should be used for cutting the sealing surface wear-resistant materials such as cobalt-based alloy or the Secretary Terai surfacing alloy. (5) of strong corrosive medium, the choice of corrosion resistant alloys must be based on media type, concentration, temperature, pressure difference, choose a suitable corrosion-resistant materials. (6) Body parts were treated with the throttle, throttle body wall and allow a certain small rate of corrosion, the corrosion rate in the LMM / years; cutting pieces by high-speed erosion, corrosion, leakage will be increased from the bow 【 large, the corrosion rate should be less than 0.1MM / year. (7) on the lining materials (rubber, plastic) of the choice of the working fluid temperature, pressure, concentration must meet the use of the material and consider it when the valve is physical, mechanical damage (such as shear failure) . (8) should not use the vacuum valve body lined with rubber, plastic structure. (9) water treatment system, two shut-off valve should not be optional rubber lining material. (10) Typical Typical corrosion resistant alloy material media options: A, sulfuric acid: 316L, Hastelloy, Alloy 20. B, nitric acid: aluminum, C4 Steel, C6 steel. C, HCl: Hastelloy B. D, HF: Monel. E, acetic acid, formic acid: 316L, Hastelloy. F, phosphate: Seoul, arising from Nickel, Hastelloy. G, urea: 316L. H, caustic soda: Monel. I, chlorine: Hastelloy C. J, water: Seoul, arising from Ni, 316L. (11) So far, the most versatile corrosion-resistant material is PTFE, known as the "King of corrosion." Therefore, we should first use corrosion-resistant PTFE valve, unusual circumstances (such as temperature "180 ℃, PN" 1.6) was selected alloy. 4, the flow characteristics of the options: Here is the initial choice, the choice of more specialized information, see: (1) S "0.6 when the election on the number of features. (2) small opening, large unbalanced force changes in the number of features selected for. (3) transfer parameters are required when the election reflects the straight-line speed, slow time selecting the right number. (4) a straight line features optional pressure regulating system. (5) an optional liquid level regulation system, a straight line features. 5, mode selection: (1) abroad on or off under the common failure to indicate that the failure to open, fault clearance, and the opening of the gas, gas, said closing the contrary, the failure to open the corresponding gas valve closed, the corresponding open air valve related failures. (2) new light valve, fine small mechanical valve has not emphasized the positive role of the Executive, reaction, and therefore must be marked in the endnotes. B (gas closed) K (open air) 6, the spring range of options: (1) First, select the spring range, but also to determine the scope of the work of the spring. (2) to determine the scope of work involved in calculating the spring force to overcome the imbalance of power output. In case of difficulties, should conditions (mainly the pressure valve is closed) to tell manufacturers to help calculate and adjusted the factory springs and scope of work (currently, many manufacturers simply do not calculate). 7, the flow of choice: (1) in the throttle, valve open against the direction of media flow away and to shut off flow of the direction of flow. (2) the choices of the flow of a single seal type valve, single seat valve, angle valve, single-sleeve valve seal three major categories. It provides the base flow (such as seat valve, V ball), and any movement (such as the O ball). (3) When the DG "15, it is usually selected away and when the DG ≤ 15 of the small-caliber valve, especially the optional high-pressure flow valve closed, to improve life. (4) two optional flow switch valve closed. (5) If the flow of closed-type valve to oscillate, change over, open-type flow can be eliminated. 8, the choice of filling: (1) is commonly used PTFE valve "V"-shaped filler and graphite "O"-shaped filler. (2) PTFE packing friction is small, but the temperature difference, short life; graphite packing friction, but the temperature, long life; high temperature and with the proposed election of the valve positioner graphite packing. (3) If the PTFE packing often change, you might consider packing with graphite. 9, attachment options: (1) the annex to the main control valve are: positioning, converters, following the drive, boost valve, to secure his position valve, relief valve, filter, lubricator, limit switch, position the sender, solenoid valves, hand wheel. (2) features and accessories to complement the role of ensuring valve operation. Necessary to increase, not to increase unnecessarily. Necessary, increase prices and reduce the annex would increase reliability. (3) Locator main function is to increase the output force and velocity, do not need those features, do not take, not like with the locator. (4) rapid response system, not the fast valve, optional converter. (5) where strict proof, optional: electrical converters + pneumatic positioner. (6) solenoid valve should be selected and reliable products to its action does not prevent action. (7) is not recommended on important hand wheel mechanism to prevent human malfunction. (8) provided by the manufacturer and the best in the valve assembly on the supplier to ensure the reliability of the system and assembly connection. (9) ordering, provide attachment name, type, specifications, input and output signals. (10) and then repeat: Please note that these "little things" the importance, in particular the reliability, if necessary, supporting air components, such as solenoid valves.

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