Venturi differential pressure flow meter does not return to 0

Thread Content

There is now a venturi differential pressure flow meter as shown in the figure below. Range: 0–1000 Nm?/h. Differential pressure range: 0–10 kPa. On-site display: 107.7√; display on the main unit: 107 Nm?/h. Since it is a pipeline related to the process and no gas is flowing through it (under normal conditions), the value should be 0. At the site, turning off the three valve assemblies stops the meter from functioning; the gauge pointer does not return to zero. It will only return to zero after the exhaust plugs on both sides are opened, but it still shows a reading of 20–30 for a while. The drainage ports on both sides are not blocked (gas can be discharged), and no leaks were found during the pipeline leak test. When the gauge is read again, it still shows a value of around 100. Even after closing the valves at the pressure-taking point, the same reading remains. Closing the three valves in that valve group does not cause the gauge to return to zero; however, closing the three valves on the negative pressure side does make it return to zero. Closing the three valves on the positive pressure side has no effect, and when those valves on the negative pressure side are reopened, the value returns to its previous level. 1. At first, I suspected that the low-signal cut-off value was too low; upon checking the configuration on the computer (Emerson system), the LOW_CUT value shown was 0.07. I think it should be 70, as a cut-off of 7% is usually used. 2. But why doesn’t the gauge on the three-valve stop unit return to zero? Even if the process specifications are incorrect and there is gas inside, why doesn’t the gauge reset on its own? It’s necessary to open the plug again. And sometimes when the plug is removed, it goes from 0 to around 30 and then back to 0? (It has nothing to do with anti-air and low-cut, right?) ) 3, Could it be that the valve on the negative pressure side of the three-valve assembly is leaking? Why does this value appear as soon as the valve on the negative pressure side of the three-valve assembly is opened? Can someone help answer this? Thank you so much! ! !