Why can't the electromagnetic flowmeter be installed at the inlet of the pump

　　Precautions for the installation of electromagnetic flowmeter clearly point out that the electromagnetic flowmeter cannot be installed at the inlet of the pump. What is the reason? In field application, the flowmeter is often installed in series with the pump on the same pipe, and the distance between them is long or short, but the electromagnetic flowmeter cannot be installed at the inlet of the pump. Because when the pump is running, when the pump starts running or the pipe wall, there will be negative pressure in the measurement pipe of the electromagnetic flowmeter. The negative pressure will accumulate in the fluid measurement pipe. If the negative pressure in the pipe reaches a certain state, the pipe lining will blister or even fall off. Therefore, the electromagnetic flowmeter cannot be installed at the inlet of the pump. If the electromagnetic flowmeter needs to be installed on the same pipe as the control valve, the electromagnetic flowmeter needs to be installed upstream of the control valve. This is to avoid the error caused by the overflow section of the electromagnetic flowmeter is not full when the flow regulating valve is adjusted. A concept should be clarified here. The control valve is not a stop valve. The stop valve should be added before and after the flowmeter and control valve. Generally speaking, if there is both flowmeter and control valve 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 way to control the valve in front and the flowmeter in the back. The advantage of this is that in many cases, the flowmeter will be sensitive to pressure changes. When the control valve is added to the front, most of the pressure drop is on the valve, and the flow measurement in the back will be stable. But the problem is that the measurement lags behind the control, that is, you can't control the flow measured by the flowmeter. It flows to the back, which is unfavorable in control. Therefore, in most cases, the control valve should be placed behind the sensor.