Determine the installation position of the negative pressure flange for a double-flange level gauge
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As shown in the diagram, the positive-pressure flange of the double-flange LT-40101 is installed properly at the bottom of the condensate tank, but the negative-pressure flange is installed on the outlet pipe of the tank. Why is it installed in this way? Is the differential pressure still calculated based on the flange spacing?
From your diagram, it appears that the transmitter’s negative pressure pipeline is not at the outlet. Additionally, the negative and positive pressure pipelines are marked with a cross, which likely indicates that they have been canceled.
The cross mark is a legend, representing the capillary.
Capillary filled with silicone oil. . . . . :L
The negative pressure side can be located anywhere where it is possible to accurately detect the pressure inside the tank; it only affects the amount of migration (that is, the zero point). As for the total measurement range and the differential pressure value, these should be determined according to the design specifications – the height of the actual measurement range should be chosen, and this is unrelated to the installation location of the negative pressure chamber. There’s also a note labeled NOTE 3 above; it’s advisable to read it carefully, as it likely explains why this specific location is chosen for the negative pressure side
There should be no problem with this. The negative pressure side of the transmitter is connected to a pipe at equal pressure, which is equivalent to the pressure inside the container; it’s only the installation height that affects the amount of migration. Since this is just a flow diagram, it’s not possible to determine how much migration will occur
It might be related to the process requirements; the pipes installed on the negative pressure side have slopes, presumably to guide the fluid flow. Therefore, the height that the level gauge needs to measure is up to those pipes, not just the liquid level in the tank.
I think it’s possible to do this; when calculating the differential pressure, the liquid level isn’t related to the distance between the flanges. The pressure at the full capacity liquid level of the container represents its range, and in worst case a correction can be applied
Assume that the contents of the tank are water, the density of the capillary silicone oil is 1, the full-scale liquid level in the container is 2 m, and the height of the flange on the negative pressure side above the pipeline is 3 m. If the transmitter’s zero point is -30 kPa when it is installed on a pipeline, then the range should be set to -30 to -10 kPa. Is this what you mean by migration?