Can a control valve with a larger diameter than the pipe still be used properly?
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In previous engineering designs, the calculated diameter of control valves was always less than or equal to the diameter of the pipes. Instrument engineers generally believed that if the calculated diameter of a control valve was larger than that of the pipe, the valve would not be able to perform its regulating function; in such cases, the process engineering team would be asked to modify the valve’s process parameters. However, I spoke with a reputable technician from a well-known foreign valve manufacturer, who said that it is still possible for a control valve to function properly even if its nominal diameter is larger than that of the pipeline. This situation occurs rarely, but it does happen, and there are successful cases of such use. This situation occurs when the Cv value is high and high precision in regulation is required; as a result, angle-type control valves fail to meet such precision requirements, so it is necessary to use globe valves with larger diameters that have been enlarged for installation. This involves some theoretical knowledge of fluid dynamics; due to my poor understanding of such theories, I am also unable to refute this technician’s claims based on principles. I hope you all can offer your advice
The diameter of the connection pipe for control valves is usually smaller than that of the pipeline, but there are exceptions. For example, when the calculated differential pressure across the valve is small.
It’s probably a valve calculation issue; no other fluid dynamics problems are involved
It can be used. Although it is not common. When a very small pressure difference before and after the valve is allowed, valves such as ball valves and butterfly valves, which have a relatively low pressure drop, are usually used. On the other hand, due to their complex flow channels, straight-stroke valves still experience a certain pressure drop or resistance even when fully open, which limits the increase in the Cv value. If straight-stroke valves are to be used, since the flow area of such valves is annular, the ways to change this flow area are either to adjust the diameter of the valve seat or to change the size of the valve core. Valve manufacturers have n sets of valve spools and seats suitable for various Cv values and flow characteristics; if requirements go beyond these series, redesign and testing from scratch are necessary, which is extremely costly and the outcomes are uncertain. Just as when a valve with a low Cv value is required, one chooses a valve whose diameter is smaller than that of the pipe, in cases where the Cv value is not high enough, choosing a valve with a diameter larger than that of the pipe is a common solution. Theoretically, as long as the Cv value meets the requirements, it makes no difference whether the valve diameter is larger than or smaller than the pipe diameter. In fact, when the valve diameter is larger than the pipe diameter, it is best to leave sections of pipe at both ends of the valve that have the same diameter as the valve.
The difference between usable and good, and the distinction between individual cases and generalities.
The concept of a control valve being “usable” should be that, within the flexible range of process operation, the control loop can operate automatically, and the deviation of the controlled parameter meets the design requirements. The control loop is a dynamic process, and it is necessary to evaluate the operating range. If only single-point operations are considered, then a flow-limiting orifice plate can be used in place of a control valve, and factories would not need to assess the \"automation rate\" either. In your example, the pressure drop distributed by the control valve is low, while the pressure drop along the pipeline is quite high (as in long-distance pipelines). Using rotary valves such as butterfly valves might allow for a reduction in diameter at a lower cost, but their control range is relatively narrow, and it does not meet the required flow variation ranges specified by the process. As a result, a GLOBE valve was chosen; its control range is larger than that of butterfly valves, although its diameter is larger than that of the pipeline. If operations involving flow rate changes are not taken into account, then a butterfly valve or ball valve can be chosen, as long as the maximum flow rate is satisfied. It means: as long as you are full, there’s no need to eat well. The pressure drop across the control valve is equivalent to the share count, while the actual flow rate through the valve corresponds to the stock price. If the pressure drop assigned to the control valve is small (i.e., few shares), how can I then cause a change in the flow rate (stock price)? ? ? ;P
In other words, as long as the calculation for selection is correct, does reducing the diameter and expanding it yield the same results in terms of performance?