原文：
               1引言　　哈尔滨气化厂是一个利用煤加压气化工艺生产煤气的化工企业，自动化水平较高，在过程控制中，执行器的控制品质与生产工况的稳定有着密切的联系，所以对执行器的选择显得格外重要，对于安全防爆要求比较高的化工企业，绝大多数执行器采用的是气动调节阀。 　　气动调节阀的选择一般要从以下几个方面进行考虑：　　1)根据工艺条件，选择合适的调节阀结构和类型。　　2)根据工艺对象，选择合适的流量特性。　　3)根据工艺参数，计算流量系数，选择阀的口径。　　4)根据工艺要求，选择材料和辅助装置。 　　下面针对以上4点加以论述。

        　　2调节阀的结构和类型　　气动调节阀是由气动执行机构和阀两部分组成的，气动执行机构是接收输入的气源信号，产生相应的推力，使推杆发生位移，推动阀门动作；而阀是指与管路联接的阀体组件部分，它接受执行机构的推杆推力，改变阀杆位移，从而改变阀门开度，最终控制流体流量的变化。　　气动调节阀按其行程可分为直行程和角行程两种，按其结构类型分直通单座阀、直通双座阀、高压阀、角形阀、套筒阀、隔膜阀、蝶阀、减压阀偏心旋转阀等。其中直通阀比较常见，单座阀泄漏量较小，但阀前后压差不能太大，而双座阀正好与之相反。高压阀适合于高静压和高压差的介质测量，但在高压差情况下，流体对材料冲刷和气蚀严重，一般要考虑阀芯和阀座的材质，以提高其使用寿命。在高压差、高黏度、含悬浮物和颗粒状物质流体的控制中可选用角形阀。隔膜阀更适用于强酸、强碱等强腐蚀性介质的控制。蝶阀适用于大流量、低压差的气体介质。套筒阀采用平衡型阀芯结构，具有低噪声的特点，是应用较为广泛的阀之一。　　气动调节阀有气开与气关两种类型。确定调节阀开关方式的原则是：当信号压力中断时，应保证工艺设备和生产的安全。如果阀门在信号中断后处于打开位置，流体不中断最安全，则选用气关阀；如果阀门在信号压力中断后处于关闭位置，流体不通过最安全，则选用气开阀。如加热炉的燃料气或燃料油管路上的调节阀，应选用气开阀，当信号中断后，阀自动关闭，燃料被切断，以免炉温过高而发生事故；锅炉进水管路上的调节阀，应选用气关阀，当信号中断后，阀自动打开，仍然向锅炉内送水， 呼吸阀 可以避免锅炉烧干。

         　　3调节阀的流量特性　　调节阀的流量特性是指介质流过阀的相对流量Q与阀芯相对行程己(阀门的相对开度)之间的函数关系：　　Q=f(L) 　　当调节阀两端压差△P保持不变时，阀的流量特性称为固有流量特性。固有流量特性主要有直线、等百分比(对数)、抛物线和快开等4种类型 　　在生产中阀的固有流量特性有直线、等百分比和快开3种。抛物线特性介于直线和等百之间，一般用等百特性来代替。快开特性主要用于二位式控制。　　在一般情况下，阀两端压差不可能永远保持不变，这时阀的固有流量特性就会发生畸变，阀在实际工作条件下的特性称之为工作流量特性。这时在确定流量特性时要引入一个称为阀阻比的系数S。　　S=△P/∑△P 　　∑△P为系统总压差，是阀、全部工艺设备和管路系统上的各压差之和。

        　　从以下3个方面内容对阀的工作流量特性进行分析： 　　1)从控制系统的控制质量方面分析　　对于一个简单的控制系统，它是由控制对象、变送器、调节器和调节阀几个基本环节组成的，系统的总放大系数K=K1K2K3K4K5 　　K1~K5分别表示变送器、调节器、执行机构、阀、控制对象的放大系数。在负荷变动的情况下，要使控制系统能保持预定的控制指标，希望总放大系数在控制系统的整个操作范围内保持不变。一般来说，在一个确定的系统里，K1~K3的系数是固定不变的，只有对象的放大系数X5随负荷的变化而变化，为此选择适当的流量特性来丰I、偿对象特性的变化，保证K4K5的乘积是个常数就保证了系统的总放大系数K是个稳定值。 　　2)从工艺配管情况分析　　调节阀总是与管道、设备连在一起使用的，管道阻力的存在必然会使阀的工作特性与固有特性不同。所以，应根据对象的特性，选择合适的工作特性，再根据配管情况选择相应阀的固有流量特性。考虑工艺配管情况时，可参照表3—1来选择阀的固有特性。衬氟蝶阀　　表3—1配管状况表　　配管状况S=1~0.6 S=0.6~0.3 S＜0.3阀的工作特性直线等百分比直线等百分比不宜控制阀的固有特性直线等百分比等百分比等百分比不宜控制　　从表3—1上看，当S=1~0.6时，所选固有流量特性和工作流量特性一致。当S<0.3时，特性曲线畸变严重不宜控制。 　　3)从负荷变化情况分析　　直线特性调节阀在小开度时流量相对变化量大，过于灵敏，容易引起振荡，阀芯阀座易损坏，故在S值小、负荷变化幅度大的场合不宜采用。等百分比阀的放大系数随阀门行程增大而增大，流量相对变化量恒定不变。

        　　4调节阀的口径　　调节阀口径的确定是在计算阀流量系数CV的基础上进行的。流量系数的定义是指在阀门全开条件下，阀两端压差△P为100 kPa，调节阀 流体密度ρ为1g／cm3时，通过阀的流体体积流量为Q(m3／h)，其节流公式为：　　C是一个比例系数，它与流量系数的关系是m倍，即CV=mC。当流量特性为直线型时m=1.63，当流量特性为等百分比型时m=1.97。　　式(4--1)是当测量介质为液体时的计算方法，当测量介质为气体时应考虑温度和压力对介质体积的影响，其C值的计算分两种情况：　　当阀前后压差△P小于0.5倍的阀前压力P1，即△P<0.5P1时 　　另外，当介质为过热蒸汽时，计算C值要考虑蒸汽的过热度。　　确定完CV值以后，要对调节阀的开度进行验算，要求最大流量时阀开度不大于90%，最小流量时开度不小于10%。在正常工况下，阀门开度应在15%~85%之间。最后根据CV值确定调节阀口径。 　　5调节阀的材料和辅助装置　　调节阀的阀体一般选用铸铁材质，其耐压等级、使用温度范围、耐腐蚀等方面应不低于对工艺管道的要求，但在介质为易燃易爆的流体时应作特殊考虑。阀芯、阀座材质的选用应考虑到流体中是否有固体颗粒产生的磨损和气蚀作用对阀内件的冲击。一般对于非腐蚀性流体，常选用不锈钢；对于腐蚀性较强的流体，锻钢阀门可选用哈氏合金；对于冲击、振动、磨损严重的流体，可选用堆焊硬质合金或喷涂材质。另外当操作介质温度高于+200℃时，要选择带散热片的上阀盖。　　调节阀的辅助装置主要有阀门定位器、电磁阀、回讯开关、过滤减压器、保位阀等。

        　　阀门定位器是调节阀的一个重要附件，常见的有气动阀门定位器和电气阀门定位器两种。它主要用于：　　1)高压差的场合；　　2)高压、高温或低温介质的场合；　　3)介质中含有固体悬浮物或黏性流体的场合；　　4)调节阀口径较大的场合；　　5)实现分程控制；　　6)改善调节阀的流量特性。　　电磁阀的作用是快速地切断和接通气源，针型阀使阀处于完全通、断的位置，多用于安全放空阀。回讯开关是需要在控制室实时监测到阀位的信号才选用的。保位阀的选择是根据工艺状况，当气源切断时，阀位要求保持在一定的位置上，但这种情况不多见。

  　　6结束语　　调节阀是自动控制系统中一个重要的环节，若选择计算不准确，使用维护不得当，将直接影响控制系统的控制质量，甚至造成严重的生产事故。为此，对调节阀的正确选用、安装和维修等各项工作都必须高度重视。　　随着工业自动化的发展，对气动调节阀的要求越来越高，这些要求包括：新结构、新材料、高性能、与计算机通讯以及优越的动态性能等。因此，对新型调节阀的研究和学习是一项艰巨而重要的任务。

“ Control loop pneumatic control valve selection method ”是由中国调节阀网提供的国际阀门新闻，译文仅供参考。另外，中国调节阀网还提供相关产品搜索： CV3000调节阀、 电动调节阀、 气动调节阀 水力调节阀、 执行器和附件等。

译文：
          1 Introduction Harbin Gasification Plant is a coal pressure gasification process used to produce town gas chemical industry, high level of automation in process control, actuator control production quality and the stability condition closely, so the choice of actuator is particularly important, safety explosion-proof requirements for relatively high chemical companies, most of the actuator is a pneumatic valve used. Pneumatic control valve selection generally be considered from the following aspects: 1) According to the process conditions, select the appropriate structure and type of valve. 2) According to the process object, select the appropriate flow characteristics. 3) According to the process parameters, calculation of flow coefficient, select the valve diameter. 4) According to the technological requirements, selecting materials and accessories. The following should be discussed for more than 4 points. 2 Structure and type of control valve Pneumatic control valve is a pneumatic actuator and the valves of two parts, the pneumatic actuator gas source for receiving input signals, resulting in a corresponding thrust, so putting shifted, push the valve action; and the valve is connected with the pipeline The body component part of its acceptance of the implementing agencies of the putter thrust to change the valve stem displacement, thereby changing the valve opening, the ultimate control of fluid flow changes. Pneumatic control valve according to stroke WATER POWER CONTROL VALVE can be divided into two straight stroke and angle of travel, type of their structure, through single-seat valve, through engine valves, high pressure valves, angle valves, sleeve valves, diaphragm valves, butterfly valves, eccentric rotation valve. Valve through which the more common, single-seat valve leakage is small but not too much pressure valve before and after, and two-seat valve just the opposite. High-pressure valve for high static pressure and pressure differential of media measurement, but in the pressure differential, the fluid and gas corrosion serious erosion of the material in general to consider the valve core and valve seat materials, to improve their life. The pressure differential, high viscosity, suspended solids and granular material with fluid control valve can be selected angular. Diaphragm is more applicable to acid, alkali and other strong corrosion control. Butterfly valve suitable for high-volume, low pressure difference of gas medium. Sleeve valve spool with balanced structure, with low noise characteristics, is one of the valves that are widely used. Pneumatic valve with air to open and air to close two types. Determine the mode switch valve principle is: When the signal pressure is interrupted, should ensure the safety of equipment and production technology. If the valve is open after the interruption in the signal position, the fluid does not break the most secure, then use air to close valve; if the pressure valve in the signal after the interruption in the closed position, fluid is not through the most secure, then use air to open valve. Such as gas or fuel oil furnace fuel valve control on the road, should be used to open gas valve, when the signal failure, the valve automatically shut down, fuel is cut off to prevent accidents furnace temperature is too high; boiler water FILTER SERIESinlet valve on the road should be used in air to close valve, when the signal failure, the valve automatically opens, still within the boiler water to avoid the boiler Shaogan. 3, the flow control valve characteristics Control valve flow characteristics is the medium flow through the valve spool relative flow Q and the relative stroke had (relative valve opening) between the functional relation: Q = f (L) When the pressure regulating valve △ P remains the same at both ends, the valve flow characteristic as the inherent flow characteristics. There are inherent linear flow characteristic, such as percentage of the (log), parabola, and 4 types such as quick Inherent in the production of valve flow characteristics are linear, equal percentage and quick opening 3. Between linear and parabolic features such as 100, and the average with the other 100 features instead. Quick Open feature is mainly used for two-type control. Under normal circumstances, the valve can not always maintain the same pressure at both ends, then the natural flow characteristics of valve distortion occurs, the valve in the actual working conditions of the properties known as work flow characteristics. Then determine the flow characteristics in the introduction of a known valve when the coefficient of drag ratio S. S = △ P / Σ △ P Σ △ P is the system total pressure difference is valve, all process equipment and piping systems and the pressure difference. From the following three aspects of the work on the valve flow characteristics of the analysis: 1) from the control system of quality control For a simple control system, which is a control object, the transmitter, regulator and control valve consisting of a few basic links, the system's total amplification factor K = K1K2K3K4K5 K1 ~ K5, respectively, transmitter, controller, actuator, valve, control object magnification factor. In the case of load changes, make the control system to maintain a predetermined control target, a wish for magnification factor in the control system within the entire operation remains the same. In general, in a certain system where, K1 ~ K3's coefficient is fixed, only the object of the amplification factor X5 with load change, this select the appropriate flow characteristics to Fung I, compensation object properties changes to ensure that the product K4K5 is a constant to ensure the system's total amplification factor K is a constant value. 2) Analysis of piping from the process Valve always piping and equipment connected with the use of, the existence of resistance would inevitably pipe valve characteristics and the inherent characteristics of different work. Therefore, in accordance with the characteristics of the object, select the appropriate operating characteristics, and then select the appropriate circumstances in accordance with control valve flow characteristics inherent. Consider the situation of process piping, refer to Table 3-1 to select the inherent characteristics of the valve. Fluorine valve Table 3-1 Status table piping Piping condition S = 1 ~ 0.6 S = 0.6 ~ 0.3 S <0.3 valve operating characteristics such as percentage ofBALANCING VALVES the straight line control valve equal percentage inherent characteristic not linear equal percentage equal percentage equal percentage should not be controlled Judging from Table 3-1, when the S = 1 ~ 0.6, the selected inherent flow characteristics and flow characteristics of the work of the same. When S <0.3, the characteristic curves should not control a serious distortion. 3) Analysis of changes from the load Linear features in a small valve opening relative changes in volume when the flow is too sensitive and prone to oscillation, valve seat easily damaged, so small in the S value, the load should not be changed much by the occasion. Amplification factor equal percentage valve with the valve travel increases, the relative variation of flow is constant. 4 caliber valve Valve diameter to determine valve flow coefficient is calculated based on the CV. Flow coefficient is defined in the valve fully open conditions, the valve pressure difference at both ends of △ P as 100 kPa, fluid density ρ is 1g/cm3, through the valve of the fluid volume flow Q (m3 / h), the section current formula is: C is a proportional factor, the relationship between it and the flow coefficient is m times, that is, CV = mC. When the flow characteristics are linear when m = 1.63, when the flow characteristic is equal percentage type when m = 1.97. Type (4 - 1) is the time when measuring the liquid medium is calculated, when measured as a gas medium temperature and pressure should be considered in the impact on the medium size, the C values calculated at the two situations: When the valve before and after the pressure △ P less than 0.5 times the valve before the pressure P1, that is △ P <0.5P1 pm In addition, when the medium is superheated steam, the calculation of C value to consider the superheat steam. After determining the value of complete CV, to the opening of the valve was checked, the maximum flow required valve opening is not more than 90%, minimum flow opening is not less than 10%. Under normal conditions, the valve opening should be between 15% to 85%. Finally, determine the value of control valve CV caliber. 5 valve materials and assistive devices Regulating valve body is generally used in cast iron, the pressure level, temperature range, corrosion resistance and so should not be less than the requirements of the process pipe, but the fluid in the medium to be explosive for special consideration. Spool, the valve seat material selection should take into account whether there is fluid in solid particles generated by wear and tear gas etching effects impact on theAPI CAST STEEL VALVES trim. General for non-corrosive fluids, are often used in stainless steel; for corrosive fluids, optional Hastelloy; for shock, vibration, wear serious fluid, or spray can be used carbide surfacing material. Also when the temperature is above +200 ℃ operating medium, we must chose to take the heat sink on the valve cover. Auxiliary equipment control valve main valve positioner, solenoid valve, echo switch, filter pressure reducer, to secure his position valve. Valve positioner is an important regulator valve attachment, common pneumatic valve positioner and two electric valve positioner. It is mainly used for: 1) The pressure differential of the occasion; 2) high-pressure, high or low temperature medium occasions; 3) medium containing suspended solids or viscous fluid situation; 4) The larger diameter valve occasions; 5) to achieve sub-process control; 6) to improve the control valve flow characteristics. The role of valve quickly cut off and connected to gas supply, the valve is fully pass, off position, and more for the safety off valve. Echo switch is needed in the control room to monitor real-time signal to the valve position was chosen. Paul places the choice of valve is based on process conditions, when the air supply cut off, the valveFORGED STEEL VALVES position required to maintain a certain position, but this is rare. 6 Conclusion Automatic Control System Control Valve is an important part, if you choose not accurate calculation, operation and maintenance shall not be treated, will directly affect the control system of quality control, and even serious accidents in production. To this end, the correct selection of the control valve, installation and maintenance work must be high priority. With the development of industrial automation, pneumatic control valve of the increasingly high demand, these requirements include: new structures, new materials, high performance, and computer communications, and superior dynamic performance and so on. Therefore, the new control valve and learning is a difficult but important task.

原文来源：http://www.1tiaojiefa.com/

2010-08-23 08:45

返回