Regarding the issue with the control valve bypass
Thread Content
That’s right; in the design documents, I’ve seen cases where the diameter of the bypass pipe for the control valve is reduced, as well as cases where it isn’t reduced. I’d like to ask the experienced folks here: what determines whether there will be a reduction in diameter? Also, what is the purpose of reducing the diameter?
Whether the diameter will shrink or not is determined by the maximum flow rate of the process; this maximum flow rate determines the flow capacity CV value of the control valve
As mentioned above, the maximum flow rate determined through the process calculations is provided to the manufacturer of the control valve, and then various parameters of that control valve can be obtained. If the diameter of the control valve calculated to be necessary is smaller than the diameter of the pipeline, a reducer is usually used; in that case, the diameter of the bypass connection can be the same as that of the control valve； If the size of the control valve is the same as that of the pipeline, there is no need for reducing the diameter; you should check that the size of the PID bypass is consistent with the diameter of the control valve~
In other words, when the control valve fails, the maximum flow rate of the bypass manual valve should also be the same as that of the control valve, right?
I see! I always thought that the bypass route had a smaller diameter by default, and that’s what I specified in my own design documents as well. . . So the root cause lies here; thank you very much
It depends on the flow rate; adjusting after diameter reduction yields better linearity.
I don’t understand this question either; I’m learning * now.
First, check what the flow rate in the bypass is, and then see what pressure is available in the bypass. If all the flow is routed back through the bypass, the piping can be made smaller since the head required for the bypass pipeline is lower, thereby saving on construction costs. Of course, when the diameter is small, the flow rate increases, but it still needs to remain within an acceptable range. If the design flow rate for the bypass route is low, the pipe diameter will naturally be small.
Whether to use a bypass neck, as well as the diameter of the upstream and downstream shut-off valves, are all determined based on the relationship between the main pipe diameter and the regulator valve diameter; each facility should have corresponding piping specifications. Additionally, when there are no special requirements for P&ID and U&ID drawings, if the DN of the bypass valve is ≤150, a globe valve should be selected ； For DN≥200, gate valves can be selected.
The throat of the control valve itself is also at least one size smaller than that of the main pipe