Why is the electromagnetic flowmeter installed upstream of the control valve?

Firstly, the electromagnetic flowmeter must be full to measure the accurate flow. The upstream of the flow regulating valve is installed to avoid the error caused by the flowmeter of the electromagnetic flowmeter when the flow regulating valve is not full. Here to clarify a concept, the control valve is not the valve, the valve should be added before and after the flow meter and control valve. Generally speaking, if there are both flow meters and control valves in the pipeline, basically the flowmeter is used to measure the flow, and then the control valve is used to control the flow. There is no control valve in the front, the flow meter is in the back, there is. The advantage of this is that in many cases, the flow meter is sensitive to pressure changes, the control valve is added to the front, the pressure drop is mostly on the valve, and the subsequent flow measurement is stable. But the problem is that the measurement is lagging behind the control, that is to say, the flow measured by the flowmeter is out of control, and it flows to the back, which is unfavorable in control. Therefore, in most cases, the control valve should be placed behind the sensor.

After years of experience in the field of fluid control engineering, flow meters and valves are one of the most commonly used equipment. Flowmeters and valves are often installed in series on a single pipe, the distance between them is long, but one of the problems that designers often have to deal with is whether the flowmeter is in front of the control valve. Now we have installed the electromagnetic flowmeter in the valve. In the alcohol factory, there is a way to send alcohol to vacuum distillation. In order to control the flow into the tower, a single-pass flowmeter and control valve are installed. After running for a period of time, the system found two problems. The first electromagnetic flowmeter is high, and the electromagnetic flowmeter lining is foamed and partially falls off. The reason is that when the control valve is controlling the flow rate, it is inevitable that sometimes the opening degree is small or all of it is closed, so the electromagnetic flowmeter measures a negative pressure in the pipe. The occurrence of negative pressure causes the dissolved gas of the fermentation liquid of the fluid measuring tube to be released. The gas in these fermentation broths causes a build-up of negative pressure in the tank. If the negative pressure in the pipe reaches a certain state, it will easily cause the pipe lining to fall off. Therefore, we generally do a good analysis according to the requirements of the pipeline and on-site requirements for better installation and use.