Design problem of the minimum flow line for centrifugal pumps
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Can the flow-limiting orifice plate on the minimum flow line be removed? To determine an appropriate pipe diameter at the minimum flow rate, it’s sufficient to use a shut-off valve; this is what we usually do in design, and limited-flow orifice plates are not seen in any engineering examples either. I can’t understand what the rationale is for such a requirement (adding flow-limiting orifice plates). I hope everyone can give some advice
We didn’t add any in practice either; it’s sufficient to calculate the minimum flow rate of the pump and select the appropriate sizes for the pipes and valves. Is the orifice plate you mentioned located on the heating pump line?
Reply to 2# Jiangtai Ren: It is on the pump return pipeline.
Some design firms include it, while others don’t; personally, I think as long as the diameter of the flow pipe is properly designed, there’s no need to add orifice plates
The poster’s approach can indeed achieve the goal. But I believe the purpose of adding orifice plates to the pipeline is: 1) to control the flow rate of backflow; the orifice plates, when calculated properly, ensure that the flow rate is appropriate, thereby avoiding waste caused by excessive backflow. 2) Functions of reducing voltage and stabilizing current. Asami, I hope the experts will bring out their best treasures.
Using a minimum return line combined with a flow-limiting orifice plate is a common practice in domestic design; its main purpose is to ensure a sufficient pressure drop, so that the minimum return line can just accommodate the pump’s minimum flow rate. If the flow-limiting orifices are removed and flow control is relied on solely on the valve, the backflow volume cannot be determined since the valve opening can vary. Especially during normal operation, the manual valve is kept fully open; with the flow-limiting orifice in place, this ensures that the backflow volume is controlled and does not become excessive. Therefore, a minimum return line together with a flow-limiting orifice plate constitutes the minimum requirement; however, many large pumps are designed to use flow control valves to regulate the return flow, especially when multiple pumps are operating simultaneously or when variable-frequency motors are used. Relying solely on valves and pipelines to reduce pressure and limit flow is not feasible.
I thought that using a flow control plate on the smallest return line would be much cheaper than using valves. Additionally, if valves are used, placing the flow control plate in front of the valves can reduce the erosion exerted by the fluid on those valves
The flow-limiting orifice plate is certainly useful for restricting the minimum flow rate and preventing excessive backflow, but it can be removed, as pumps rarely operate at the minimum flow rate; opening the circulation valve slightly when the flow is low is sufficient.
Our company’s gas distribution device is equipped with a minimum flow line, on which a flow orifice plate is installed. In this way, the traffic remains stable and the operations are easy to carry out. It is recommended to use an orifice plate.
The diagram on page 37 of HG20559-1993 shows the stop valve in front; can this be interpreted as reducing the erosion of the flow control plate, thereby decreasing the need to replace it? I wonder what everyone’s thoughts are?