The choice of regulating valve type: (1) to determine the nominal pressure, not to use Pmax set PN, but by the temperature, pressure, material three conditions from the table to find the corresponding PN and meet the selected valve PN value. (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. Need to consider three issues: a. Simple structure (the simpler the more reliable), easy maintenance, spare parts have a source; b. 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. Valve actuator choice: (1) the most simple is the pneumatic film, followed by the piston, the last is 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) old ZMA, ZMB film actuator can be eliminated, replaced by a multi-spring light actuator (performance improvement, weight, height reduction of about 30%). (5) piston actuator more variety, old, large and stupid proposal is no longer selected, and use light new structure. Control valve material selection: (1) 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) For cavitations, 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 be used 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.
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