Seeking help regarding the diameter change of control valves
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Between the DN50 pressure reducing valve and the DN50 control valve, there is a pipeline of over 1 meter in length along with 2 shut-off valves. The original PID had the diameters changed to DN65 both before and after the pressure reducing valve as well as before and after the control valve; I want to change it to DN50 to avoid having 2 such diameter changes. Two shut-off valves reduce the diameter by one size; may I ask if this modification is acceptable? If there’s no such way, I’ll give up too and stop seeking out the Master of Techniques.....
Control valves are usually adjusted by one size step; with these two diameter changes, no savings are possible~
I know that it’s usually a reduction in diameter, but these two are too close together... so I have some thoughts on it
According to available information, reducing the diameter of a control valve by one size category is intended to increase the linear velocity of the fluid and thus the pressure drop, which facilitates more accurate regulation by the control valve. Therefore, the pipe diameter is reduced by one size grade before and after the control valve. As for the pipe diameter, it should be calculated to suit the flow rate required for the fluid to function properly, resulting in low pressure losses and efficient operation. Therefore, apart from control valves and the like, it is best to maintain the original pipe diameter.
Theoretically, the control valve has a diameter one size smaller than that of the main pipe. The nominal diameter DN65 should be calculated based on a reasonable flow velocity. In your case, with such a short distance, changing the diameter of the pipe in between to DN50 should not pose any problems. It’s just that the flow rate is a bit higher. If it is media such as water, nitrogen, steam, or wind, there’s no problem at all. Be cautious if the medium is a flammable gas such as hydrogen, as there are requirements regarding the maximum flow rate for hydrogen.
You want to modify the pipe, right? Make it have the same diameter as the valve opening to avoid the need for a reducer; it should work fine if there’s no pressure regulator.
First, it is cheap, as there is a large price difference compared to control valve power units and actuators； Secondly, the smaller diameter results in a lower pressure drop in the pipeline and a higher pressure drop at the valve; as a result, when making adjustments, the flow curve of the entire pipeline becomes more similar to the flow regulation curve of the valve
1. If the medium is not flammable or explosive, it can be changed; however, an increase in line speed poses safety risks. 2. If it belongs to a pressure pipeline, the design institute needs to issue a change order. 3. Ensure that there is no cross-connection at the control valve
Reducing the diameter of the pipeline between the shut-off valve and the control valve is equivalent to reducing the diameter of the main pipe, which is not allowed per the process requirements. The pressure drop increases.