Troubleshooting abnormal liquid level gauge readings
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There is one condensate flash tank in one of the plant’s unit areas; the operating pressure is 0.4 MPa. The fluid handled is steam condensate. The tank is equipped with one dual-flange differential pressure level gauge (Yokogawa EJA118W) and one magnetic flap level gauge. Both level gauges indicate a height of 1.2M. The double-flange level gauge (which has been relocated) now shows a reading that fluctuates between 80% and 85%. However, when the valve is opened to drain the liquid, only steam comes out, yet the level gauge still indicates a level fluctuating between 80% and 85%. The magnetic flap level gauge either shows no reading or it displays the full scale. At full scale, the root valve was closed and the level gauge drain was opened; only a little water flowed out, with the rest being steam (leakage in the root valve). Question: 1. Why does the double-flange level gauge fluctuate only between 80% and 85%? 2. There isn’t too much water in the magnetic flip valve, so why is it showing full scale? Those who have encountered similar situations, please explain. Thank you!
1. Turn on the drainage; if steam comes out, it indicates that the tank is empty. If the gauge still shows around 80%, something is not right. It’s better to remove the gauge and check whether the zero point is correct and whether the linear response is normal. 2. It’s possible that the liquid level fluctuates too much and too quickly, exceeding the reaction speed of the magnetic flip switch.
On the one hand, your double-flange level gauge should be recalibrated (for zero point and range). On the one hand, it might be that the magnetic flap level gauge on site has moved, and you need to add insulation and heating.
When the pressure is released, the differential pressure level reads 0, and the magnetic flap also drops back.
Based on your description, I don’t think it’s a problem with the gauge itself; rather, it’s likely an issue with the medium. You’ve tried to drain it, but no liquid comes out – only steam. Both of these instruments are level gauges designed to measure liquid levels, and since the medium in question could be steam or a mixture of steam and liquid, the instruments certainly won’t function properly. It’s recommended to consult the process engineers to conduct a thorough inspection and determine the exact nature of the medium, so that a solution can be found
It’s a strange phenomenon; from your description, it seems that the pressure is higher at the bottom and lower at the top of your condensate container. . Only in this way will what you mentioned occur: the transmitter also shows a liquid level, and the magnetic flip switch is pushed to the highest position as well. . .
Reply to 6# cjsh12345: I agree with the view expressed on floor 6. Sometimes we shouldn’t assume that there’s something wrong with the instrument just because its readings appear abnormal; in many cases, it’s the process conditions that cause incorrect readings. In the poster’s case, it’s very likely due to the operating conditions – ask more questions about the operation process and learn more about the relevant techniques. Those working in the field of instruments should consider whether the process conditions might be affecting the instruments when problems occur, as there are fewer conscientious operators these days.
Based on what you provided, it should be a process issue! The medium is not just water; it includes saturated vapor as well! At this point, the range P = (p_water + p_saturated_vapor) / 2 * g * h; the migration amount can be read directly from 475!
It is recommended to remove the gauge: 1. Check the zero point； 2. What material is the gasket made of? Is there a diaphragm box? What you measured was the level of condensed steam water; this phenomenon occurs when tetrafluoroethylene is used, as in that case it’s all steam at a liquid level of 0. At high temperatures, the gasket deforms, which affects the diaphragm box. I have encountered similar situations in routine maintenance work.
This is a bit complicated. First, what is zero after the pressure is removed? Is it range or differential pressure? If the range is zero, then it’s correct; if the differential pressure is zero, then it’s incorrect. Think about this ； Also, from your description, it’s pretty clear that the liquid level is very low, but the impact is strong. I wonder what the structure of your device is like – at least what its shape is I keep feeling that the impact is too great; why not use a glass tube level gauge to actually observe the true condition of the liquid surface?