Orifice plate flow meter
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The valve is closed; the differential pressure of the orifice flow meter is -4.4 kp, and the flow rate shows zero. During operation, the flow rate of the flow meter rose suddenly from 500 m3/h to 900 m3/h, remained at that level for about ten minutes before dropping to zero. Does anyone know what’s going on in this situation?
One of my clients is facing the same issue, which has not been resolved yet. The flow meter used is a small piston-type one installed on the equipment; the flow meter itself is fine, but the flow rate is not stable. Could it be that the valve is preventing a stable flow rate? Waiting for the answer together with the original poster
Please specify whether it is the pressure tapping valve of the differential pressure flow meter or the flow control valve on the process pipeline. If it is a flow control valve installed in the process pipeline, and the differential pressure is negative when the valve is fully closed, then is the pump on the process pipeline located below the flow meter? If it is the pressure-taking valve of a differential pressure flow meter, a negative value appears when it is fully closed; one possible reason is severe leakage at the positive-pressure side of the pressure-taking valve ； Second, there is a leak at the flange on the positive side of the differential pressure flow meter ； Third, the positive side of the three-valve assembly (or five-valve assembly) is blocked. It is also possible to experience the aforementioned phenomenon of an empty pipe inside the pipeline at very low flow rates, due to the installation location of the pump. First, try to turn off the three-valve assembly and loosen the vent screw of the differential pressure transmitter, so that the positive and negative pressure chambers are fully connected to the atmosphere; at this point, the transmitter should output 4mA. In other words, the differential pressure is zero, and the flow rate reading is also zero. If, with all valves in the three-valve assembly closed and both the positive and negative pressure chambers fully connected to the atmosphere, the differential pressure transmitter still shows a negative value, there is a problem with the transmitter; it must be recalibrated or replaced.
First, think carefully about whether the operation of your three valve assemblies for opening and closing is correct. Check the three-valve assembly again. Measure again whether the change in the differential output is consistent with the change in the flow integrator. The cause still cannot be identified after these steps. Contact me
Waiting for the answer together with the original poster