Thread Content
When magnetic flap level gauges were first introduced, they were installed and used in positive-pressure environments. For the measurement of liquid levels in open systems, such as water and sewage, it usually involved ordinary liquids that were neither viscous nor crystalline. With the continuous development of industry and the increasing demands on production processes, production technologies have kept advancing. Magnetic flap level gauges have gradually come to be used in situations involving liquids with high viscosity and under negative pressure. Although these gauges can now handle negative-pressure level measurements without any problems, the various complex factors associated with negative pressure conditions can affect accurate measurement if not taken into account. This article analyzes the typical faults that occur when using magnetic flap level gauges in negative-pressure environments, outlines approaches to resolving them, and proposes corresponding solutions to help users improve their ability to identify and fix such issues. Given the advantages of magnetic flap level gauges, such as complete isolation between the medium being measured and the indicating mechanism, excellent sealing performance, leak prevention, and the ability to measure liquid levels in corrosive environments, along with their high reliability, good vibration resistance, simple structure, easy installation, and low maintenance costs, they are now widely used in industries such as electricity, petroleum, chemicals, metallurgy, environmental protection, shipbuilding, construction, and food processing. Our client, a company in Shanghai, uses magnetic flap level gauges with remote transmission for measuring the levels of brine, distilled water, and condensed water in systems for seawater desalination using heat compressors in low-temperature multi-effect distillation processes. To prevent scaling, it is necessary to bring seawater to its boiling point at low temperatures, which requires a negative pressure inside the seawater desalination system; under normal operation, this pressure is around -0.093 MPa. This is the process requirement that must be met when using magnetic flap level gauges. The following explanation provides an analysis of typical failure scenarios involving air leakage in the pipelines when the gauge is operating under negative pressure. I. Description of the fault phenomenon: The brine level gauge in the main unit U3 of the seawater desalination system began to show fluctuations of 30%–70%. Upon inspection, no abnormalities were found with the gauge itself. After reducing the valves at the top and bottom of the gauge, the fluctuations in level measurement decreased, but the fault phenomenon persisted. Take advantage of the blast furnace shutdown to reduce the main load on the seawater desalination U3 unit and identify the cause of the fault. Close both the upper and lower valves on the level gauge, remove the lower plug, open the drain valve to thoroughly exhaust and remove debris, and inspect the magnetic float – no abnormalities were found. Fluctuations occur after it is put into operation. After replacing the brine level gauge and attempting to restart operation, it was found that the level indication provided by the gauge fluctuated more significantly and more frequently. Upon inspection, it was found that there was a leak at the weld of the pipe connected to the liquid level measurement container (see Figure 1). After sealing this leak, the liquid level readings returned to stability, and normal production under load resumed. II. Analysis of the cause of the fault In reality, the actual level of the concentrated brine did not fluctuate at the time of the fault; however, the float inside the magnetic flap level gauge did move up and down, thereby creating an illusion of a fluctuating liquid level. After closing the valve on the magnetic flap level gauge, the fluctuations ceased, which indicates that the upward and downward movement of the float is caused by the interaction between the gas-water mixture and the negative pressure environment. That is, gas enters from the bottom of the magnetic flap level gauge, causing the float to rise. The upper part of the magnetic flap level gauge is in contact with a negative-pressure environment; when the gas inside the gauge penetrates the water surface and is drawn into this negative-pressure environment, its volume decreases, which causes the float to drop back down. This process repeats itself, creating an illusion of fluctuating liquid levels. III. Proposed solutions: (1) During maintenance, not only should the magnetic flap level gauge itself be inspected, but all connecting pipes and flanges as well. Given the corrosiveness of concentrated saltwater, the pipelines connected to the level gauge should be replaced regularly. (2) When fluctuation in the liquid level display occurs in a magnetic flap level gauge under negative pressure, it can be analyzed and resolved following the steps below. ①First, check the display of the magnetic flip switch on the level gauge; if the display is stable, then there is a problem with the level transmitter unit or the signal transmission circuit. Next, measure the current signal output by the Jiangsu Evergrande level transmitter, as well as the current signal output by the power distribution isolator in the control cabinet, to determine whether everything is functioning properly and thus identify the source of the fault. ②If the reading shown by the magnetic flap level gauge is consistent with the readings on the upper-level display and the fluctuations are not severe, first close the valve that connects the level gauge to the measuring container, and open the drain valve to release waste fluid. At the same time, check whether there are any problems with the float itself of the level gauge. If there are no issues, then examine whether there are any leaks at the upper and lower plugs of the level gauge, as well as at the drain valve and the connection flanges. Also, observe the fluctuations in the level gauge by adjusting the opening degree of the upper and lower valves. The quality of the level gauge can be determined through the above measures. ③Check for leaks in the liquid level measurement container and connecting pipes. For more information, please visit the company’s official website at http://www.yb1518.com/. Please retain this link when reproducing the content! http://www.yb1518.com/uploadfiles/image/2010-11//201011191011384084.jpg