Dual-flange differential pressure level gauge
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The distance between the upper and lower flanges of the double-flange differential pressure level gauge is 0.8 meters; the transmitter is installed slightly below the lower flange. With the root valve fully opened and the vent also fully open, the transmitter shows -7.5 kPa. Why is the value negative? During installation, the high-pressure measurement flange is at the bottom and the low-pressure measurement flange is at the top. This level gauge is used to measure the liquid level; the media are water and gasoline. Could the technicians please explain what the zero point and the range are? How is it calculated? Thank you
The zero point needs to be calculated by oneself, as does the range. The pressure displayed currently, plus the pressure when the tank is full of gasoline, gives the zero point; the pressure displayed currently, plus the pressure when the tank is full of water, gives the range.
Is it correct to display a negative pressure of -7.5 kPa?
There’s no problem with that; this pressure is a differential pressure, which is the positive pressure minus the negative pressure. Since the tank is empty, there is also a pressure difference due to the height of the capillary tube (P=ρgh), and the pressure at the top is certainly higher than that at the bottom, so it’s normal for a negative value to be displayed.