Regulating valve diameter change issue
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The system I’m working in features many sections where the pipe diameter changes; after such changes, control valves are used to adjust the diameter, for example, changing it from 3 inches to 1.5 inches. However, after just over 2 years of operation, more than 20 of these control valves have failed due to high flow rates and the corrosive nature of the medium used. All of them were Fisher brand valves, and I think this represents a significant waste. I would like to ask why control valves are needed after the pipe diameter is changed. If I were to cut out those sections with altered diameters and replace them with control valves of 3-inch diameter, what parameters should be taken into account when selecting such valves? I know how to calculate the relevant formulas. Additionally, will replacing the valves with 3-inch ones affect the flow characteristics of the original pipes? Please give your advice
It will affect the original traffic characteristics. After switching it back, first of all, the resistance of the entire piping system decreases, while the so-called pressure drop across the control valve – a value that actually represents the resistive force involved in regulating the flow rate through the control valve – increases. -------Just trying to stimulate some discussion. The above is for reference.
By doing the calculations, it can be seen that for a certain flow rate/pressure difference, there is a specific Cv value; the Cv value chosen corresponds to the diameter of the valve. For a given diameter, there is also a corresponding degree of valve opening. If the diameter is changed from 1.5 inches to 3 inches, the biggest problem is that it becomes impossible to adjust the valve opening, as it ends up being too small and thus not within the normal operating range. Recommendation: Do not change the valve diameter; instead, consider changing the material of the valve body or valve core.
Indeed, the pipe diameter should not be changed arbitrarily; it is determined through calculations. If a change is desired, professional assistance is needed to conduct the calculations in order to determine it. It’s better to change the material.
Indeed, changing the material selection is the simplest method, but I think the material of our control valves is already very good; the leakage is probably caused by too high a flow rate. I’ll keep researching this further. .
Changing the pipe diameter affects regulation, and it can be adjusted accordingly based on the opening degree of the control valve.
The pipe diameter of the control valve is determined through calculations based on process requirements, taking into account the impact of flow velocity on the valve. Changing the pipe diameter arbitrarily can affect the control performance and process stability. It is necessary to consider whether the process conditions specified when selecting the control valve match the actual conditions, as well as whether the selected materials meet the requirements of those process conditions.
The valve internals can remain unchanged while the valve body diameter can be increased.
When designing and selecting control valves, it is required that their diameter be one size smaller than that of the pipeline they are connected to; therefore, a diameter reduction is necessary. This not only improves the sensitivity of the control performance but also helps to reduce costs