Is the flowmeter reading low or high when the orifice plate is installed backwards?
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This post was last edited by xxkhc on 2016-3-11 22:15. Regarding the issue of the orifice plate being installed in the wrong direction, the statements in the books I’ve read vary; for example: 1. Many books state that when the orifice plate is installed incorrectly, the flow meter’s readings are lower. 2. The book “200 Questions and Answers on Industrial Automation Instruments and Their Systems” states that when a flow meter is installed with the orifice plate in the reverse orientation, the readings are too high; when it is installed with the nozzle in the reverse orientation, the readings are too low. The Venturi tube is somewhat similar to the orifice plate, but the issue of abnormally high flow meter readings is not as severe as with the orifice plate. Both of these two different views are supported by theoretical calculations. So who is right after all? Has anyone ever conducted experiments to determine the errors that occur when an orifice plate is installed in the correct or reversed orientation under the same operating conditions? Are only measurement departments and manufacturers equipped to carry out such experiments?
Based on the flow diagram of the orifice plate, if the orifice plate is installed in the reverse direction, the measured value should be higher. But some sources say the measured values are on the low side.
If the orifice plate is installed in the reverse direction, the pressure difference corresponding to the same flow rate is lower, resulting in a lower reading on the flow meter. This is absolutely correct and has been proven in practice. If you don’t believe it, go and experiment for yourself.
If the reverse pressure is set too low, then the flow rate will naturally be low
It’s definitely on the small side; as for the reason, I don’t know~
I thought about it: under the same operating conditions, with a constant pressure difference before and after the orifice plate, reversing the orientation of the orifice plate will result in an increased actual flow rate, as the resistance coefficient decreases. With the same signal, a reversed orientation leads to a higher flow rate; in other words, if the flow rate remains the same, the flow signal will be lower when the orifice plate is reversed.
That’s right, as said upstairs! ! That’s probably how it is; it’s just that the starting point mentioned in the book is different, which has led to the original poster’s misunderstanding!
The orifice plate measures the hydrostatic pressure of the fluid against the pipe wall. Due to the orifice plate’s obstruction of the fluid flow, some of the fluid flowing upstream of the orifice plate flows back, and this backflow creates additional pressure on the side walls of the upstream pipe. The static pressure measured by the orifice plate actually includes this \"additional\" pressure. (This is different from taking pressure samples using a pressure transmitter.) ISO requires that the upstream inlet of the orifice plate be a \"vertical sharp angle\" (while a chamfer may be present on the downstream side), in order to maintain accuracy in pressure measurement upstream (as this was stipulated in the original testing standards). If there is reverse flow (upstream chamfering), the pressure measurement upstream decreases, and the flow rate also becomes lower. One can take a look at the pressure distribution diagrams upstream and downstream of the flange-mounted pressure tap; there is an \"upward jump\" in the pressure value upstream of the orifice plate, and this is the reason for it. @jiaguoyun @Big Horse with Big Bow