For several years, people have considered several traditional factors when choosing a control valve, such as pressure rating, pressure drop, flowing medium, temperature, and cost. However, the situation has changed greatly over the past 10 years. Many advances have been made in the design of valves. The cost-effectiveness of production processes is quite different from before, which has made many of the traditional factors that had to be considered when selecting valves. The importance has been greatly reduced.
Dynamic characteristics
Although some traditional factors are still important, they only emphasize the "static" performance of the valve. In fact, they are the results obtained by measuring the valve on the "workbench", but it is difficult to say what kind of performance the valve will exhibit under actual operating conditions. Traditional theory believes that careful adjustment of static factors will result in good performance of the valve (and therefore of the entire circuit). However, we now realize that this is not always the case.
Thousands of performance checks conducted by researchers and manufacturers have demonstrated that as many as 50% of the valves in use (many of which are selected by considering conventional factors) have not had much effect on optimizing control loop performance. Subsequent studies have shown that the dynamic characteristics of the valve play an important role in reducing process variability. In many key processes, different valves can reduce the variability of the process, even if the difference is 1%, can greatly increase production efficiency and reduce waste, so that more than one million US dollars of economic benefits can be achieved. Obviously, such economic benefits allow us to completely negate the traditional practice of deciding whether or not to purchase only based on the initial purchase price of the valve.
Second, the traditional view always holds that the improvement of the process optimization always comes from the upgrade of the control instrument in the control room. However, the test data shows that the dynamic characteristics of the valve can have a significant effect on loop performance under the same control instrumentation. If the accuracy can only reach 5%, then spending a lot of money to configure a set of advanced control instrument systems whose control accuracy can reach 0.5% does not play a significant role.
Valve type
When looking for a valve that matches the use situation, the four basic types of throttle control valves, caged ball valve, rotary ball valve, eccentric valve, and butterfly valve, should be examined first.
The wide range of tabs for caged ball valves can meet the needs of most applications, making it the first choice for a wide range of valves. There are many kinds of cage ball valve adjustment pieces, including balance adjustment piece, unbalance adjustment piece, elastic seat adjustment piece, constrained adjustment piece and full-size adjustment piece. In many cases, the various tab configurations of a valve body are interchangeable.
Caged ball valves also have several disadvantages. First, the size of the valve is limited (usually 16 inches); Second, compared with the same size of the line of sight valve (such as ball valve or butterfly valve), its capacity is relatively low; Third, the price is higher, especially large Caliber cage ball valve. However, cage valves have excellent performance in reducing process variability and are often sufficient to compensate for these deficiencies.
The flow of the rotary float valve is larger than that of a cage valve of the same diameter. Although the control range of the rotary float valve is larger than that of the cage ball valve, the uniform swing Pang Biaomu ______________ ____________________________________________ /m2, suitable for use at temperatures below 398°C. Float valves are not suitable for liquids that are prone to cavitation, and they can often give off louder noise when used in gases with higher pressure drops.
Eccentric valves have lower friction and lower prices than float valves. The unique structural design makes it more accurate for the control of process variability. This is evident from Fisher's new product, the BV500. In addition, the advantages and disadvantages of the eccentric valve are not much different from those of the float valve.
According to the performance of the valve, the butterfly valve is a low-range valve. The butterfly valve has a large flow, the cheapest price, and a variety of different calibers. However, the characteristic curve of the butterfly valve has only one kind of proportional characteristic curve, which greatly restricts the performance of the butterfly valve to reduce process variability. For this reason, butterfly valves can only be used in applications where the load is constant. Although butterfly valves come in a variety of different calibers and can be made from most cast alloys, butterfly valves do not meet ANSI requirements for face to face dimensions, and are not suitable for fluids that are prone to cavitation or where noise is high. .
Dynamic characteristics
Although some traditional factors are still important, they only emphasize the "static" performance of the valve. In fact, they are the results obtained by measuring the valve on the "workbench", but it is difficult to say what kind of performance the valve will exhibit under actual operating conditions. Traditional theory believes that careful adjustment of static factors will result in good performance of the valve (and therefore of the entire circuit). However, we now realize that this is not always the case.
Thousands of performance checks conducted by researchers and manufacturers have demonstrated that as many as 50% of the valves in use (many of which are selected by considering conventional factors) have not had much effect on optimizing control loop performance. Subsequent studies have shown that the dynamic characteristics of the valve play an important role in reducing process variability. In many key processes, different valves can reduce the variability of the process, even if the difference is 1%, can greatly increase production efficiency and reduce waste, so that more than one million US dollars of economic benefits can be achieved. Obviously, such economic benefits allow us to completely negate the traditional practice of deciding whether or not to purchase only based on the initial purchase price of the valve.
Second, the traditional view always holds that the improvement of the process optimization always comes from the upgrade of the control instrument in the control room. However, the test data shows that the dynamic characteristics of the valve can have a significant effect on loop performance under the same control instrumentation. If the accuracy can only reach 5%, then spending a lot of money to configure a set of advanced control instrument systems whose control accuracy can reach 0.5% does not play a significant role.
Valve type
When looking for a valve that matches the use situation, the four basic types of throttle control valves, caged ball valve, rotary ball valve, eccentric valve, and butterfly valve, should be examined first.
The wide range of tabs for caged ball valves can meet the needs of most applications, making it the first choice for a wide range of valves. There are many kinds of cage ball valve adjustment pieces, including balance adjustment piece, unbalance adjustment piece, elastic seat adjustment piece, constrained adjustment piece and full-size adjustment piece. In many cases, the various tab configurations of a valve body are interchangeable.
Caged ball valves also have several disadvantages. First, the size of the valve is limited (usually 16 inches); Second, compared with the same size of the line of sight valve (such as ball valve or butterfly valve), its capacity is relatively low; Third, the price is higher, especially large Caliber cage ball valve. However, cage valves have excellent performance in reducing process variability and are often sufficient to compensate for these deficiencies.
The flow of the rotary float valve is larger than that of a cage valve of the same diameter. Although the control range of the rotary float valve is larger than that of the cage ball valve, the uniform swing Pang Biaomu ______________ ____________________________________________ /m2, suitable for use at temperatures below 398°C. Float valves are not suitable for liquids that are prone to cavitation, and they can often give off louder noise when used in gases with higher pressure drops.
Eccentric valves have lower friction and lower prices than float valves. The unique structural design makes it more accurate for the control of process variability. This is evident from Fisher's new product, the BV500. In addition, the advantages and disadvantages of the eccentric valve are not much different from those of the float valve.
According to the performance of the valve, the butterfly valve is a low-range valve. The butterfly valve has a large flow, the cheapest price, and a variety of different calibers. However, the characteristic curve of the butterfly valve has only one kind of proportional characteristic curve, which greatly restricts the performance of the butterfly valve to reduce process variability. For this reason, butterfly valves can only be used in applications where the load is constant. Although butterfly valves come in a variety of different calibers and can be made from most cast alloys, butterfly valves do not meet ANSI requirements for face to face dimensions, and are not suitable for fluids that are prone to cavitation or where noise is high. .
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