Control valve selection precautions

The choice of valve type: (1) Determine the nominal pressure, instead of using pmax to cover pn, but find the corresponding pn from the table under the three conditions of temperature, pressure and material, and satisfy the pn value of the selected valve. (2) to determine the type of valve, the amount of leakage to meet the technical requirements. (3) to determine the type of valve, the working pressure should be less than the valve to allow the pressure difference, if not, then from a special point of view or choose it valve. (4) medium temperature in the valve operating temperature range, ambient temperature to meet the requirements. (5) consider the problem of anti-blocking valve according to the media is not clean. (6) According to the chemical properties of the valve consider the corrosion resistance of the valve. (7) Consider valve erosion and wear resistance based on differential pressure and hard media. (8) Considering the economic performance, the price ratio. Three questions need to be considered: a. Simple structure (the more simple the higher reliability), easy maintenance, spare parts have a source; b. Service life; c. price. (9) Preferred order. Butterfly Valves - Single Seat Valves - Double Seat Valves - Stem Valves - Angle Valves - Three Way Valves - Ball Valves - Eccentric Rotary Valves - Diaphragm Valves. The choice of implementing agencies: (1) the most simple is the pneumatic film, followed by the piston, and finally the electric. (2) The main advantage of the electric actuator is that the driving source (power) is convenient, but the price is high, reliability, waterproof and explosion-proof than the pneumatic actuator, so pneumatic should be preferred. (3) The old electric actuator is bulky, and we already have the electronic compact and highly reliable electric actuator (the price is high accordingly). (4) The old zma, zmb film actuator can be eliminated, replaced by a multi-spring light actuator (performance improvement, weight, height decreased by about 30%). (5) piston actuator more variety, old, large and stupid proposal is no longer selected, and use light new structure. Material selection: (1) The valve body pressure level, temperature and corrosion resistance and other aspects should not be less than the requirements of the process of connecting pipes, and should be preferred factory stereotypes. (2) Water vapor or moisture containing more water and flammable and explosive media, cast iron valve should not be used. (3) When the ambient temperature is below -20 ℃ (especially in the north), cast iron valves should not be used. (4) cavitation, erosion is more serious medium temperature and pressure in Cartesian coordinates, the temperature is 300 ℃, the pressure difference is 1.5mpa two points outside the connection area, the throttle sealing surface should Selection of wear-resistant materials, such as cobalt-based alloy or surface surfacing Secretary Telai alloy. (5) Corrosive medium, the choice of corrosion resistant alloy must be based on the type of media, concentration, temperature, pressure, select the appropriate corrosion-resistant materials. (6) The valve body and throttling pieces are treated separately, the valve body inner wall throttling speed is small and allows a certain degree of corrosion, the corrosion rate can be about lmm / year; throttling pieces are subject to high-speed erosion, corrosion will bow Large, the corrosion rate should be less than 0.1mm / year. (7) The choice of lining materials (rubber, plastic) temperature, pressure, concentration of the working medium must meet the scope of the use of the material, and consider the physical and mechanical damage (such as shear damage) . (8) vacuum valve should not use the valve body lined with rubber, plastic structure. (9) two shut-off valve water treatment system should not use lining rubber material. (10) Typical Corrosion-resistant Alloy Material Selection for Typical Media: a. Sulfuric acid: 316l, Hastelloy, No. 20 alloy. b. Nitric acid: aluminum, c4 steel, c6 steel. c. Hydrochloric acid: Haste's b. d. Hydrofluoric acid: Monel. e. Acetic acid, formic acid: 316l, Hastelloy. f. Phosphoric acid: Because Nickel, Hastelloy. g. Urea: 316l. h Caustic soda: Monel. i. Chlorine: Hastelloy c. j. Sea water: because of nickel, 316l. (11) So far, the most versatile corrosion-resistant material is PTFE, known as "Corrosion Resistant King." Therefore, the first choice of all PTFE corrosion valve (Hualin patented product), the last resort (such as temperature> 180 ℃, pn> 1.6) before the selection of alloys. The choice of flow characteristics: The following provides a preliminary choice, see the specific choice of specific information: (1) s> 0.6 when the election logarithmic characteristics. (2) a small opening work, change of unbalance force large number of logarithmic characteristics. (3) When asked to be transferred to reflect the parameters of the speed of the election straight line, slow logarithm of the election. (4) pressure regulating system optional linear features. (5) Level adjustment system optional linear features. The choice of mode of action: (1) open or close commonly used fault abroad to indicate that the fault open, fault off, and our gas open, gas closed that the exact opposite, the fault open corresponding to the gas valve, the fault off the corresponding gas valve . (2) The new light valve, fine valve has no emphasis on the positive role of the implementation of machinery, reaction, and therefore must be marked on the endnote. The choice of spring range: (1) First, select the spring range, but also to determine the working spring range. (2) Determining the working spring range involves calculating the output force to overcome the unbalanced force. If there is any difficulty, the conditions (mainly the pressure difference when the valve is closed) should be informed to the manufacturer to help calculate and adjust the spring and working range of the factory (at present, many manufacturers do not make calculations at all). The choice of flow: (1) In the throttle, the flow of the medium against the valve core in the direction of opening flow, flow direction to the closure of the flow closure. (2) the choice of flow is mainly single sealed type regulating valve, a single-seat valve, angle valve, single-sealed sleeve valve three categories. It is for the specified flow (such as double-seat valve, v-ball) and arbitrary flow (such as o-ball). (3) When dg> 15, usually choose to open, when dg ≤ 15 small-diameter valves, especially high-pressure valve optional flow-off, in order to improve life expectancy. (4) The two on-off valve optional flow closed. (5) If the closed-flow valve oscillation, change over, open-type can be eliminated. Filler choice: (1) Regulating valve is commonly used PTFE "v" -shaped packing and graphite "o" -shaped packing. (2) PTFE packing friction, but the temperature difference, short life expectancy; graphite packing friction, but good temperature, long life; high temperature and with the valve positioner recommended graphite packing. (3) If PTFE packing often change, you can consider using graphite packing. Accessories options: (1) control valve accessories are: locator, converter, relay, booster valve, relief valve, pressure reducing valve, filter, oil mist, limit switch, the location of the sender , Solenoid valve, hand wheel mechanism. (2) Accessories function as supplementary functions and ensure valve operation. Necessary to increase, unnecessary increase. Adding attachments when not needed increases the price and reduces reliability. (3) The main function of the positioner is to increase the output force and speed of movement, without these functions, you can not take, not with the locator just fine. (4) Fast response system, do not valve action fast, optional converter. (5) Strict explosion-proof occasions, optional: electrical converter + pneumatic positioner. (6) Solenoid valve should choose a reliable product, to prevent it from moving action. (7) Important occasions suggest not to use hand wheel mechanism to prevent human action. (8) It is best to be supplied by the manufacturer and the assembly is supplied on the valve to ensure the reliability of the system and assembly connection. (9) When ordering, the name, model, specification, input signal and output signal of the accessory should be provided. (10) reiterated: Please note the importance of these "little things", especially the reliability, if necessary, Hualin can be matched with Japanese pneumatic components, such as solenoid valve