Cascade control

Thank you all. After discussing it in the group, no one has seen this approach used before. In my opinion, the change in pressure difference before and after the valve after pressure regulation has a significant impact on flow rate; therefore, it’s likely not feasible to implement this method

I haven’t seen it; usually, within the same pipeline, the process control focuses on those process parameters that require the most stability. In cascade control, the flow rate is generally part of the secondary loop, and its role is relatively minor. . . If it is necessary to control both pressure and flow at the same time, pressure control will definitely be the choice. Once the pressure is under control, the flow will also be stable, so there is no need for any cascade control. This type of cascade control should lead to parameter coupling, causing the valve to remain in a constant state of operation. What you say makes sense as well: the calculations take into account the maximum closing differential pressure, but in reality the differential pressure before and after the valve is variable. As a result, when the valve is adjusted, the system pressure within the pipeline keeps changing, and so does the flow rate; it’s impossible to achieve proper control

I want to know how pressure on a pipeline is controlled. Is it done using valves? It doesn’t seem so; valves are generally used to control flow rate. Even if they do affect pressure, it is the flow rate that is controlled, and this in turn influences pressure – there is no specific relationship between valves and pressure. So, if you’re worried about excessive pressure, add a safety valve

Under normal circumstances, pressure regulation is achieved by adjusting the flow rate; therefore, it is not necessary to use a cascade control system for pressure regulation； Conversely, to ensure stable flow regulation, the upstream pressure must be stable; otherwise, it is difficult to maintain stable flow. Furthermore, since the pipe resistance changes with flow rate, it is difficult to set fixed values for pressure at different flow rates, which makes implementing a cascade control system challenging. Moreover, there is really no need for this; if one needs to control the flow rate, that’s enough – if pressure control is also required, simply add another control loop.