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Technical analysis: Evaluating the dynamic characteristics of control valves is crucial. For years, when selecting control valves, people have taken into account various traditional factors such as pressure rating, pressure drop, flow medium, temperature, and cost. However, much has changed over the past 10 years; significant progress has been made in valve design, and the cost-effectiveness of production processes is very different from before. As a result, the importance of many traditional factors that used to be essential when choosing valves has **diminished**. Dynamic characteristics: Although some traditional factors remain important, they focus only on the valve’s “static” performance. In fact, they are the results obtained by measuring the valves on a \"workbench,\" but such results make it difficult to determine what performance the valves will exhibit under actual operating conditions. Traditional theory holds that carefully adjusting the static factors will enable the valve (and thus the entire circuit) to achieve good performance. However, we now realize that this is not always the case. Thousands of performance tests conducted by researchers and manufacturers have shown that up to 50% of the valves in use (many of which were selected based on traditional factors) fail to have much impact on optimizing the performance of control loops. Subsequent studies have shown that the dynamic characteristics of the valve play a significant role in reducing process variability. In many key processes, even a 1% difference in the extent to which different valves reduce process variability can significantly improve production efficiency and reduce waste, thereby generating economic benefits of over $1 million. Obviously, such economic benefits allow us to completely reject the traditional approach of deciding whether to purchase a valve based solely on its initial purchase price. Secondly, the traditional view has always been that improvements in process optimization stem from upgrades to the control instruments in the control room. However, test data show that, under the condition of using the same control instruments, the dynamic characteristics of the valve can have a significant impact on the performance of the loop. If the precision of the control valve can only reach 5%, then spending a large amount of money on a sophisticated control instrument system with a precision of 0.5% will not be very effective. Valve types: When looking for a valve that is suitable for a particular application, one should first consider the 4 basic types of throttle control valves, namely cage ball valves, rotary float valves, eccentric valves, and butterfly valves. The types of adjusting elements available for cage ball valves are extremely diverse, allowing them to meet the requirements of most applications; this makes them the preferred choice among various types of valves. There are many types of adjusting plates for cage ball valves, including balanced adjusting plates, unbalanced adjusting plates, elastic seat adjusting plates, constrained adjusting plates, and full-size adjusting plates. In many cases, various adjustment plate configurations for a single valve body can be interchanged. Cage ball valves also have several disadvantages. First, the size of this valve is limited (usually 16 inches); second, its capacity is relatively low compared to sight valves of similar specifications (such as float valves or butterfly valves); third, it has a high price, especially for large-diameter cage ball valves. However, in terms of reducing process variability, cage ball valves exhibit excellent performance, which is often sufficient to compensate for these drawbacks. The flow rate of a rotary float ball valve is higher than that of a cage ball valve of the same diameter. Although the control range of the rotary ball valve is greater than that of the cage ball valve, it still outperforms most other types of valves. The allowable pressure drop and allowable temperature range of the rotary ball valve are lower than those of the cage ball valve. Typically, their maximum pressure drop is 7.0x105 kg/m2, making them suitable for use at temperatures below 398°C. Float valves are not suitable for liquids prone to bubbling, and when used with gases at high pressure drops, they often generate significant noise. Eccentric valves have less friction than ball valves and are cheaper. Its unique structural design enables more precise control over process variability. This is evident in Fisher’s new product, the BV500. Other than that, the advantages and disadvantages of the eccentric valve are not much different from those of the float valve. Measured by the performance of valves, butterfly valves belong to the lower-grade category.