May I ask the seniors,,,
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Dear friends and seniors, why do the pipes before and after the flow meter need to have different diameters?
In the case of a rotameter, not only should there be no change in diameter, but there must also be a sufficiently long straight pipe section… In the situation you described, it’s likely that the diameters of the pipeline and those of the flowmeter do not match, with the flowmeter’s diameter being smaller.
Pipes are kept at a constant diameter, mainly to reduce pressure drop, while flowmeters have a variable diameter, primarily due to the requirements of their measurement range.
It is not specified what type of flow meter it is, what the medium is, or what the conditions at the site are. The diameter changes before and after a flow meter are usually done to suit the flow meter itself, in order to meet its measurement range and achieve the best possible accuracy in measurements. For example, if the medium does not fill the pipe completely, or if the flow rate is too high or too low, the requirements of the flow meter can be met by reducing or increasing the diameter of the pipe. However, when the diameter changes before and after, it is necessary to ensure that there is sufficient straight pipe section; otherwise, the accuracy of the flow meter will not improve but will instead decline.
Well, the installation diagrams shown in some flowmeter manuals, with the diameter changing before and after, can be quite misleading
Flowmeters have specific requirements regarding flow velocity; if it is too low or too high, accurate measurement is not possible. The flow rate of the same volume of flow is different in pipes of different diameters. So sometimes it is necessary to change the pipe diameter in order to keep the flow rate within a range suitable for measurement. Under normal circumstances, even if the flow meter has no requirements regarding straight pipe sections, diameter changes should be avoided, or straight pipe sections should be left after such changes.
The requirements of the measurement range! For electromagnetic flowmeters, flow rates outside the specified range cannot be measured.
Electromagnetic flowmeters belong to the velocity-type flowmeters, and they have requirements regarding both the upper and lower limits of the fluid velocity. Upon analysis, there may be several reasons for your situation: Horizontal installation: 1. The flow rate does not meet the requirements ； 2. The medium does not fill the pipe. Vertical installation (bottom up): 1. The flow rate does not meet the requirements
The change in diameter is intended to meet the minimum flow velocity requirement of the flow meter, which is a necessary condition for accurate measurement. If the flow velocity meets the requirements for measurement, then there is no need for a change in diameter............
To buy a size smaller flow meter and save money!