How to choose the type of regulating valve?

Selection of valve type: (1) Determine the nominal pressure, instead of removing PN with Pmax, find the corresponding PN from the table according to the three conditions of temperature, pressure and material to meet the PN value of the selected valve. (2) The determined valve leakage meets the process requirements. (3) The working pressure difference of the determined valve type should be less than the allowable pressure difference of the valve. If it is not possible, we should consider it from a special angle, or choose another valve. (4) The medium temperature is within the working temperature range of the valve, and the ambient temperature meets the requirements. (5) Consider the anti-blocking problem of the valve according to the unclean condition of the medium. (6) Consider the corrosion resistance of the valve according to the chemical properties of the medium. (7) Considering the erosion resistance of the valve according to the pressure difference and the medium containing hard objects. (8) Performance-price ratio considering comprehensive economic effects. There are three problems to be considered: a. Simple structure (the simpler the structure, the higher the reliability), convenient maintenance and spare parts; B. service life; C. price. (9) Optimal 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 one is pneumatic diaphragm type, followed by piston type and finally electric type. (2) The main advantage of electric actuator is that the driving source (power supply) is convenient, but the price is higher, and the reliability, waterproof and explosion-proof are not as good as those of pneumatic actuator, so pneumatic actuator should be the first choice. (3) The old electric actuator is huge, and we have a compact and highly reliable electric actuator (the price is correspondingly higher). (4) The old ZMA and ZMB thin film actuators can be replaced by multi-spring photo actuators (the performance is improved and the weight and height are reduced by about 30%). (5) There are many varieties and specifications of piston actuators, and the old, big and stupid suggestions are no longer selected, but a new light structure is selected. Material selection: (1) The pressure grade, service temperature and corrosion resistance of the valve body should not be lower than the requirements of the process connection pipeline, and the products of the manufacturer should be preferred. (2) Cast iron valves are not suitable for steam or moisture containing more moisture and inflammable and explosive media. (3) When the ambient temperature is below -20℃ (especially in the north), cast iron valves should not be used. (4) When the temperature and pressure difference of the medium with serious cavitation and erosion are in rectangular coordinates, the temperature is 300℃ and the pressure difference is 65438±0.5 MPa, the sealing surface of the throttle valve should be made of wear-resistant materials, such as cobalt-based alloy or stellite surfacing. (5) For highly corrosive media, the choice of corrosion-resistant alloy must be based on different types, concentrations, temperatures and pressures of the media, and appropriate corrosion-resistant materials should be selected. (6) If the valve body and the throttling part are treated separately, the throttling speed of the inner wall of the valve body is small, and some corrosion is allowed, and the corrosion speed can be around lmm// year; Throttle parts will be corroded by high-speed erosion, which will increase the leakage. The corrosion rate should be less than 0. 1mm// year. (7) When selecting lining materials (rubber, plastic), the temperature, pressure and concentration of working medium must meet the application range of materials, and physical and mechanical damage (such as shear damage) caused by valve action should be considered. (8) The vacuum valve shall not be made of rubber and plastic lining. (9) Rubber lining material is not suitable for the two cut-off valves of water treatment system. (10) Selection of typical corrosion-resistant alloy materials for typical media: A. Sulfuric acid: 3 16L, Hastelloy, No.20 alloy. B Nitric acid: aluminum, C4 steel and C6 steel. C. hydrochloric acid: Harrington B. hydrofluoric acid: monel. Acetic acid and formic acid: 3 16L, Hastelloy. Phosphoric acid: Inconel and Hastelloy. G. urea: 3 16L. Caustic soda: Monel alloy. 1. Chlorine: Harrington C.J. Seawater: Inconel, 3 16L. (1 1) Up to now, the most widely used corrosion-resistant material is tetrafluoroethylene, which is called "the king of corrosion resistance". Therefore, first of all, we should choose perfluoro corrosion-resistant valve (patented by Hualin Institute), if we have to (such as temperature >; 180℃，PN > 1.6)。 Selection of flow characteristics: The following are preliminary choices. For detailed selection, please refer to the logarithmic characteristics of special data: (1) s > 0.6. (2) When the opening is small and the unbalanced force changes greatly, the logarithmic characteristic is selected. (3) The required tuning parameters reflect a straight line at high speed and a logarithm at slow speed. (4) The pressure regulating system has optional linear characteristics. (5) The liquid level regulating system has optional linear characteristics. Choice of action mode: (1) Fault opening or closing is widely used abroad, that is, fault opening and closing are just the opposite of domestic gas opening and closing. Fault opening corresponds to gas closing valve, and fault closing corresponds to gas opening valve. (2) The new light valve and small valve no longer emphasize the positive and negative effects of the actuator, and must be marked on the endnote. Selection of B (air-closed) K (air-opened) spring range: (1) First, select the spring range and determine the working spring range. (2) Determining the working spring range includes calculating the output force to overcome the unbalanced force. If there is any difficulty, the manufacturer should be informed of the conditions (mainly the pressure difference when the valve is closed) to help calculate and adjust the spring and working range before leaving the factory (many manufacturers do not calculate at all at present). Selection of flow direction: (1) At the throttle valve, the medium flow in the opening direction of the valve core is open and the flow in the closing direction is closed. (2) The choice of flow direction is mainly single sealing regulating valve, including single seat valve, angle valve and single sealing sleeve valve. It is based on the specified flow direction (such as two-seat valve, V-ball) and arbitrary flow direction (such as O-ball). (3) When DG > 15, it is usually open; when dg≤ 15, small-caliber valves, especially high-pressure valves, can be closed to improve their service life. (4) The two-position on-off valve can be selectively closed. (5) If the closed valve swings, the open valve can be eliminated by replacement. Selection of packing: (1) PTFE "V" packing and graphite "O" packing are commonly used in control valves. (2) PTFE packing has small friction, but it is temperature resistant and has short service life; Graphite filler has large friction, but good temperature resistance and long service life; For valves with positioners at high temperature, graphite packing is recommended. (3) If PTFE packing is changed frequently, graphite packing can be considered. Accessories selection: (1) The accessories of the control valve mainly include: positioner, converter, relay, booster valve, position maintaining valve, pressure reducing valve, filter, oil mist device, travel switch, position transmitter, solenoid valve and handwheel mechanism. (2) Accessories play an auxiliary role to ensure the operation of the valve. Add what is necessary, not what is unnecessary. Adding unnecessary accessories will increase the price and reduce the reliability. (3) The main function of the positioner is to improve the output force and action speed. When these functions are not needed, it is not necessary to carry a locator. (4) For the quick response system, the switch is optional, not quick valve action. (5) In strict explosion-proof occasions, optional: electric converter+pneumatic positioner. (6) Reliable products should be selected for the solenoid valve to prevent it from not acting when required to act. (7) It is recommended not to use handwheel mechanism in important occasions to prevent human misoperation. (8) It is best to provide it by the manufacturer and assemble it on the valve to ensure the reliability of the connection between the system and the components. (9) The name, model, specification, input signal and output signal of the accessories shall be provided when ordering. (10) Again: Please pay attention to the importance of these "little things", especially the reliability. If necessary, Hualin Research Institute can support Japanese pneumatic components, such as solenoid valves. Please refer to/