Selection of control valves
Thread Content
The diameter of the pipeline for the medium circulation water is DN200. The maximum flow rate is 28,740 KG/H, while the normal flow rate is 25,000 KG/H. The density is 1,000 KG/m3. The pressure before the valve is 0.5 MPa, and the pressure after the valve is 0.4 MPa. The calculated maximum CV value is approximately 33.627, with a normal CV value of 29.2511. When checking the opening degree based on percentage characteristics, if a DN125 valve is used, the maximum opening degree is 41% and the normal opening degree is 39%. If a DN100 valve is used, the maximum opening degree is 54% and the normal opening degree is 50%. What size of valve should be chosen? Why?
This set of parameters is already quite comprehensive; it includes information on the material properties and flow rate, as well as the pressures before and after the valve. The valve manufacturer will use this information to determine the appropriate diameter for the valve, which is usually equal to the diameter of the pipeline. If high precision in adjustment is required, they will suggest a reduced diameter for the valve. Inward or outward contraction. It depends on your company’s actual requirements.
Since DN100 can meet the flow requirements and the opening degree is within a reasonable range, what’s there to worry about?
The opening size should be appropriate; the smaller the diameter, the cheaper it is. Of course, choose DN100
A DN100 valve can indeed meet the requirements, but the pipeline is DN200 – that’s a reduction of half. Is this acceptable?
I’m worried there could be other effects; the diameters of the pipes and control valves differ by too much
Thank you, expert. I work in design and need to make selections; in such situations I don’t know which option is better. If I don’t understand it, I still won’t be able to choose next time I encounter this issue
You design? I’m only responsible for selection, not manufacturing. . On our end, we also carry out the selection and design work ourselves; you just need to choose the appropriate diameter, as well as basic process parameters such as the material properties. The procurement side has completed its work.
DN100 will suffice; only a diameter reduction is required. The circulating water pipeline has such a large diameter, yet the flow rate is not high.
Roughly speaking, choose Cv at twice the calculated value. For single-seat valves, DN65 is also suitable. V-ball valves DN40 are all suitable. Ball valve DN25.
The selection of this valve was primarily determined by the conflict between the process pipeline diameter and the valve diameter; clearly, the process pipeline is too large in scale – with only a flow rate of 25 cubic meters – yet the pipeline was designed to be DN200. . . . . .