Importance of dynamic characteristics of the hotte

2022-07-26
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Importance of dynamic characteristics of control valve factory inspection of control valve mainly refers to the inspection of static characteristics, including basic error, rated stroke deviation, return difference, start and end point deviation, dead zone, repeatability error, tightness, leakage, etc. These are tests made under no-load conditions. In fact, they are the results obtained by measuring the valve on the workbench, However, such results are difficult to explain what kind of performance the valve will show under actual operating conditions. According to the traditional theory, careful adjustment of static factors will enable the valve (and thus the whole circuit) to achieve good performance in 2012. Now, however, we realize that this is not always the case

thousands of performance checks conducted by researchers and manufacturers have proved that up to 50% of the control valves (many of which are selected by considering traditional factors) have not produced much effect on optimizing the performance of the control loop. Subsequent research shows that the dynamic characteristics of the valve play an important role in reducing the process variability. In many key processes, different valves can significantly improve production efficiency and reduce waste even if they reduce process variability by 1%, thus achieving great economic benefits. Obviously, this economic benefit allows us to completely deny the traditional practice, that is, whether to buy the valve or not is determined only according to the initial purchase price of the valve

secondly, the traditional view always believes that the improvement of process optimization always comes from the upgrading of control instruments in the control room. However, the test data show that the dynamic characteristics of the valve can have a significant impact on the circuit performance under the condition of using the same control instrument. If the accuracy of the control valve can only reach 5%, then it is not necessary to spend a lot of money to configure a set of advanced control instrument system whose control accuracy can reach 0.5%. People have been exploring various experimental methods to detect the steel wire rope and trying to control the performance of the steel wire rope

when looking for a valve that matches the application occasion, we should first investigate four basic types of throttle control valves, namely cage ball valve, rotary floating ball valve, eccentric valve and butterfly valve

the cage ball valve has a wide variety of adjustment plates, so it can meet the needs of most applications, making it the first choice among various valves. There are many kinds of cage ball valve adjusting plates, including balance adjusting plate, non balance adjusting plate, elastic seat adjusting plate, constrained adjusting plate and full-size adjusting plate. In many cases, the various tab configurations of a valve body are interchangeable

cage ball valves also have several disadvantages. First, as a factory owner who has worked in Dongguan steel industry for many years, the size of the valve is limited (usually 16 inches); Second, compared with the sight valve of the same specification (such as floating ball valve or butterfly valve), its capacity is relatively low; Third, the price is high, especially the large-diameter cage ball valve. However, in reducing process variability, cage ball valves have excellent performance, which is often enough to make up for these defects

the flow of the rotary floating ball valve is larger than that of the cage ball valve with the same diameter. Although the control range of rotary ball valve is larger than that of cage ball valve, it is still superior to most other types of valves. The allowable pressure drop and temperature range of the rotary ball valve are smaller than that of the cage ball valve. Generally, the upper limit of their pressure drop is 7.0x105kg/m2, which is suitable for use at temperatures lower than 398 ℃. The ball valve is not suitable for liquids that are prone to cavitating, and it may often produce large noise when used in gases with high pressure drop

eccentric valve has less friction and lower price than ball valve. The unique structure design makes it more accurate to control the process variability. This can be seen from the new product bv500 of Fisher company in the plan. In addition, the advantages and disadvantages of eccentric valve are similar to those of ball valve

according to the performance of the valve, the butterfly valve is a low-grade valve. Butterfly valve has large flow, the cheapest price, and has a variety of different diameters. However, the characteristic curve of butterfly valve is only equal proportion characteristic curve, which greatly limits the performance of butterfly valve in reducing process variability. For this reason, the butterfly valve can only be used when the load is fixed. Although the butterfly valve has many different diameters and can be made of most cast alloys, the butterfly valve does not meet the ANSI requirements for face-to-face dimensions, nor is it suitable for fluid prone to cavitation or occasions with high noise

to sum up, the dynamic characteristics of the control valve are as important as the static characteristics, or even more important than the static characteristics, because it can better determine whether the control valve meets the requirements of the site conditions, so as to select the control valve more suitable for the site conditions for us, which requires close communication between the manufacturer and the user

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