Let’s discuss the issue of selecting the pressure difference for control valves
Thread Content
There is such a pipeline whose overall flow resistance is very low; it can be considered as
Ultimately, the choice of value depends on the pressure difference before and after the valve. The pressure difference is high, the valve opening is small, and the flow velocity is fast. The pressure difference is low, the valve is open to a large extent, and the flow rate is slow. A higher flow rate results in relatively more noise. But based on the conditions mentioned, the flow rate is not high; the pipe diameter should be below DN50. Personally, I think it’s better to use larger imported ones.
With low pipe resistance, it is likely that gas is being transported; in such cases, a pressure of 1.0 before the valve is a good choice. This results in a certain pressure difference across the valve, though it isn’t extremely large – only three times the pressure difference – which ensures that the pressure difference across the valve remains appropriate. If a pressure of 0.4–0.5 is chosen before the valve, then a larger valve size will be necessary to achieve the required flow rate, as valves inevitably cause pressure losses
On this pipeline, the flow resistance drop other than that caused by the control valve is only 0.05. If a gas supply pressure of 1.0 MPaG is used, the control valve will require 0.6 MPa of pressure; thus, the pressure drop across the control valve divided by the pipeline’s flow resistance drop equals 1200%. Wouldn’t this mean that the diameter of the control valve I end up choosing has to be smaller? Is it easy to adjust, or can it become too large or too small? If a gas source of 0.4–0.5 MPaG is selected, the pressure drop absorbed by the control valve is approximately 0.05–0.15 MPa; thus, the ratio to the flow resistance in the pipeline is not very high. Wouldn’t this result in better control performance?
What is being adjusted is the gas flow rate; since the unit used is Nm3/h, if a 1MPa gas source is chosen, the valve diameter will be very small, and the valve opening degree can fall within the favorable range of 30-70%. If a 0.4-0.5 MPa gas source is selected, then the valve cannot have a large pressure drop, so the valve diameter has to be larger
This post was last edited by zhxbkofkyo on 2022-6-8 at 14:29. It’s in the gas phase – isn’t it necessary to consider the ratio of the pressure drop across the control valve to the flow resistance loss in the pipeline? This control valve is a flow control valve; using a 1MPa air supply seems to result in an excessive pressure level. Could this make the valve too sensitive, thereby making it difficult to regulate the flow? The main goal is to maintain a stable flow rate
There is no need to consider the ratio of valve pressure drop to pipeline pressure drop; control valves are quite sensitive, and it is necessary to adjust the PID parameters in order to achieve stable flow control
0.4-0.5 is sufficient; there’s no need to increase the inlet pressure just for the control valve – that would be putting the cart before the horse