Problems with double-flange differential pressure level gauges
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Recently I encountered such a problem: one of the ammonia tank gauges in our facility has a range of 0–800 mm, and it uses a double-flange capillary differential pressure level gauge; however, negative values can sometimes appear. Everyone, please help analyze what causes this situation.
I’ve encountered similar ones; I’m not sure if they’re the same as yours? Reason: An error in the operational procedures led to a vacuum inside the equipment, which caused the diaphragm box with double flanges to deform (bulging outward; it should be flat under normal conditions). The instrument gives readings intermittently. In the end, I replaced it with another one, and it worked fine. Suggestions: 1. Check according to the condition of the process. 2. Remove the double flanges and conduct a verification. Now I know what the reason is; it’s not necessarily due to the instrument itself. 3. Check whether there are any heat sources near the positive-pressure capillary.
The capillaries on the positive and negative pressure sides should be at the same ambient temperature; otherwise, it will cause measurement errors.
Check whether the flange gasket presses against the membrane during installation, and whether the membrane is deformed. Check whether a negative pressure actually appears on the pressure gauge of the ammonia tank.
Checking the diaphragm box is the right thing to do. Generally, there are no major issues with the transmitter