How to choose the diameter of butterfly valve
In the general flow calculation process, we can divide the flow coefficient of the butterfly valve into the rated flow coefficient and the working condition flow coefficient.
The rated flow coefficient is an inherent characteristic of the butterfly valve. As long as the structure of the butterfly valve is determined, the rated flow coefficient is determined. It has nothing to do with the temperature, pressure, density, etc. of the working conditions.
C (KV), K (ζ) value of butterfly valve (JB/T 53171—1999)
| DN | ≤PN16 | PN20, PN25 | ||
|---|---|---|---|---|
| C(Kv) | K(ζ) | C(Kv) | K(ζ) | |
| 40 | 50 | 1.64 | 40 | 2.56 |
| 50 | 80 | 1.33 | 45 | 2.37 |
| 65 | 150 | 1.27 | 120 | 1.98 |
| 80 | 250 | 1.05 | 200 | 1.64 |
| 100 | 400 | 1.00 | 300 | 1.78 |
| 125 | 650 | 0.92 | 450 | 1.93 |
| 150 | 1000 | 0.81 | 800 | 1.26 |
| 200 | 1900 | 0.71 | 1500 | 1.14 |
| 250 | 3100 | 0.65 | 2500 | 1.00 |
| 300 | 4700 | 0.59 | 3600 | 1.00 |
| 350 | 6700 | 0.53 | 5400 | 0.82 |
| 400 | 9000 | 0.51 | 7000 | 0.84 |
| 450 | 11500 | 0.50 | 9500 | 0.73 |
| 500 | 14000 | 0.50 | 12000 | 0.69 |
| 600 | 21000 | 0.47 | 18000 | 0.64 |
| 700 | 30000 | 0.43 | 25000 | 0.61 |
| 800 | 41000 | 0.39 | 35000 | 0.53 |
| 900 | 53000 | 0.37 | 46000 | 0.50 |
| 1000 | 67000 | 0.35 | 68000 | 0.48 |
| 1200 | 100000 | 0.33 | 87000 | 0.44 |
The flow coefficient of the working condition is determined by the (maximum, normal, minimum) flow rate of the working condition and the corresponding working temperature, pressure before the valve, pressure after the valve, medium density and other parameters, and has nothing to do with the structure of the butterfly valve.
The selection principle of butterfly valve diameter is as follows:
- When the hidden valve is only used as an on-off valve, that is, the valve state is either fully open or fully closed, as long as the rated flow coefficient of the butterfly valve is greater than the maximum flow coefficient required by the working conditions. The valve diameter is generally the same as the nominal size of the pipeline.
- When the butterfly valve is used as a regulating valve, in addition to the rated flow coefficient of the butterfly valve being greater than the maximum flow coefficient required by the working condition, it should also be considered that due to the limitation of the butterfly valve structure, the butterfly valve has poor regulation performance at a small opening. Under the minimum operating condition, the valve opening is above 20°, and it is recommended that under the maximum operating condition, the valve opening should be below 70°. In order to achieve the throttling adjustment effect, it is generally hoped that the adjustment loss of the system should be mainly on the control valve, and the flow rate of the butterfly valve can reach about 5m/s. When the butterfly valve meets the above requirements, in many cases the valve diameter needs to be reduced (smaller than the nominal size of the pipeline), but not less than 1/2 of the nominal size of the pipeline.
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