调节阀的选型与控制常识

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原文：
选择调节阀时，首先要收集完整的工艺流体的物理特性参数与调节阀的工作条件，主要流体的成份、温度、密度、粘度、正常流量、最大流量、最小流量、最大流量与最小流量下的进出口压力、最大压差等。而在技术方面主要掌握和确定调节阀本身的结构、流量特性、额定流量系数Kv值、口径大小、工艺允许压差计算及执行机构的选择、材料和安装等方面的内容。　选择调节阀时一般应遵循的原则有如下几点。　　一调节阀的结构型式：应能满足介质温度、压力、流动性、流向、调节范围以及严密性的要求。　　二调节阀的流量特性：应能满足系统特性进行合理的补偿。　　调节阀的流量特性是指介质流过阀的相对流量与阀杆相对位移间的关系，数学表达式如下：Q/Qmax=f(l/L)，式中Q/Qmax为相对流量，为调节阀在某一开度时流量Q与全开流量Qmax之比；l/L为相对位移，调节阀在某一开度时阀芯位移l与全开位移L之比。　　选择的总体原则是调节阀的流量特性应与调节对象特性及调节器特性相反，这样可使调节系统的综合特性接近于线性。选择流量特性通常在工艺系统要求下进行，但是还要考虑下述实际情况。　　1、直线性流量特性适用范围：①差压变化小，几乎恒定；②工艺流程的主要参数的变化呈线性；③系统压力损失大部分分配在调节阀上(改变开度，阀上差压变化相对较小)；④外部干扰小，给定值变化小，可调范围要求小。　　2、等百分比特性适用范围：①实际可调范围大；②开度变化，阀上差压变化相对较大；③管道系统压力损失大；④工艺系统负荷大幅度波动；⑤调节阀经常在小开度下运行。　　3、除了以上两种常用的流量特性之外，还有抛物线特性和快开特性等其他流量特性的调节阀。　　三调节阀的口径：应能满足工艺上对流量的要求。　　根据已知的流体条件，计算出必要的Kv值，选取合适的调节阀口径。　

“ Control valve selection and common sense"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、执行器和附件、更多调节阀产品、调节阀价格等。

译文：
Control valve selection and common sense Select the control valve, the first complete collection of the physical characteristics of the process fluid control valve parameters and operating conditions, the main fluid composition, temperature, density, viscosity, normal flow, maximum flow, minimum flow, maximum flow and minimum flow rate import and export pressure, maximum pressure and so on. In the technical aspects of the main control valve itself and determine the structure, flow characteristics, the rated flow coefficient Kv value, aperture size, technology allows the calculation of pressure and actuator selection, materials and installation aspects. Select the control valve when the general principles to be followed are the following. A valve structure type: should be able to meet the medium temperature, pressure, flow, flow, adjust the scope and rigor of the requirements. Two valve flow characteristics: the system should be able to meet the characteristics of reasonable compensation. Control valve flow characteristics is the medium flow through the valve stem relative to flow and the relationship between the relative displacement, mathematical expressions are as follows: Q / Qmax = f (l / L), where Q / Qmax for the relative flow rate, as adjusted When opening the valve at a flow rate Q and the ratio of full-flow Qmax; l / L for the relative displacement of the valve when the valve opening in a displacement l and the ratio of full-shift L. The overall principle is the selection control valve regulating the flow characteristics should be the object characteristics and regulator features the contrary, it will give a comprehensive control system features close to linear. Select the flow characteristics in the process is usually carried out under the system requirements, but also consider the following facts. 1, the linear flow characteristics of the scope of application: ① pressure change is small, almost constant; ② The main process parameter changes linearly; ③ loss of most of the distribution system pressure control valve on the (change in opening the valve on the pressure change is relatively small); ④ external interference, given the value of small changes, small adjustable range of requirements. 2, the percentage of properties such as the scope of application: ① actual adjustable range; ② opening change, relatively large changes in differential pressure valve; ③ large piping system pressure loss; ④ process system load fluctuations; ⑤ valve often in small opening run. 3, in addition to the above two common flow characteristics, there are parabolic features and other features quick opening flow characteristics of control valve. Three valve diameter: should be able to meet the technical requirements on the traffic. According to the known fluid conditions, necessary to calculate the Kv value, select the appropriate valve diameter.

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原文来源：http://www.1tiaojiefa.com/

2012-01-16 08:31