Glass plate level gauge
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For a regular glass plate level gauge, is the level it displays related to the two valves above and below it? For example, the one above is not turned on while the one below is turned on; is the liquid level high or low? What about the other way around? Thank you. . .
If the pressure in the tank is positive, it should be on the high side
I have a gentle question: is the principle behind glass plate level gauges based on pressure difference or the principle of a communicating vessel? ?
It should be a communicating vessel, with the liquid level interface readable directly through the glass
It’s the principle of a communicating vessel: when the pressures are equal, the liquid levels are also equal.
The poster is referring to the magnetic flap level gauge. Its principle is as follows: when the liquid level in the container being measured rises or falls, the magnetic float inside the gauge’s tube moves up and down accordingly. The permanent magnet inside the float transmits a magnetic signal to the magnetic flap indicator, causing the red and white flaps to rotate 180°. When the liquid level rises, the flaps change from white to red； When the liquid level drops, the flip column changes from red to white ； The point where the red and white on the indicator meet indicates the actual height of the liquid level inside the container, thereby providing a clear indication of the liquid level.
If the valve above is not open, there is some gas in the upper part, and the compressed gas generates a certain pressure that must counteract the pressure resulting from the difference in liquid levels; this causes the reading to be lower. If the valve below is not open, it will be impossible to indicate the liquid level at the beginning. Once the liquid level rises to be at the same level as the pipeline of the upper valve, some of the liquid enters the gauge tube, causing the reading to increase; this results in a value that is much lower than the actual liquid level. Sometimes this can lead to a situation where the middle part of the gauge shows a white reading while the ends show red readings, resulting in malfunctioning indication.
It’s the principle of a communicating vessel; there don’t seem to be any pressure-sensing elements in it. How can differential pressure be measured?
I feel that if the valve above isn’t open, the liquid in the tower will flow into the level gauge, causing the air inside to be compressed and resulting in a low liquid level! If the valve below is not opened, full balancing cannot be achieved, as there is compressed air in the lower section, which causes the liquid level inside to be too high!
I agree with the answer from the friend on floor 8; it’s quite comprehensive and accurate.