Issue with the valve seat diameter of the control valve
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Seeking advice: Based on past experience, we chose DN25 pipes for the steam supply, but they turned out to be a bit too small; therefore we switched to DN40 steam pipes and selected corresponding control valves. The specific method for calculating the steam flow rate is as follows: Q = 0.02*0.02*3.14*16*3600*4, which is approximately 270 KG/h. (I checked that the flow velocity of steam at pressures below 1 MPA ranges from 15–20 m/s; I chose 16, with a density of around 4 kg/m3.) Thus, the normal steam flow rate is 200 KG/h, while the maximum flow rate is 270 KG/h. Question 1: Is it correct to determine the normal and maximum values of the steam flow rate based solely on the pipe specifications, and then provide these values to the control valve manufacturer? Then the manufacturer provided me with drawings; the diameter of the pipe flange interface for the valve is DN40, while the diameter of the valve seat is DN25. Question 2: Is the flow rate at a valve seat with a diameter of DN25 very high (>20 m/s or even higher), in order to meet the requirements I have? Question 3: Is the valve seat diameter generally a bit smaller than the corresponding pipe diameter calculated? Question 4: How to simply calculate the valve seat diameter for better compatibility with the pipeline?
What are the pressures before and after the control valve, and what is the temperature? If the valve manufacturer suggests that a reduction in diameter is necessary, then there is generally no problem – there’s no need to worry about that. If the diameter isn’t reduced, the valve’s opening degree will decrease, which can also cause damage to the valve
The valve seat diameter is calculated based on the process parameters you provided, and it is generally equal to or less than the pipe diameter. As long as the process parameters specified are correct, the calculation results will be accurate.
Is the amount of steam I calculated correct?
If the valve opening does not shrink, it will become smaller, which also causes damage to the valve. How should this be understood? I need guidance!
The valve seat has a large diameter; at a constant flow rate, the opening degree must be small. At a low opening degree, the erosion of the valve internals is relatively severe
Isn’t the flow velocity at the valve seat much higher than that in the pipeline?
The valve has throttling, so the flow velocity there will definitely increase, and the diameter will also become larger
The valve has throttling, so the flow velocity there will definitely increase, and the diameter will also become larger
With throttling, the flow rate will definitely increase, and the diameter will also grow; this is inevitable
Then, if I determine the flow rate based on the pipeline, this calculation should be fine, right? So, the flow rate through this pipeline is roughly that much?