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Analysis of common reasons why the flap of a magnetic level gauge does not change with the liquid level.
Time：
2026-04-22
Magnetic level gauges, with their advantages of being intuitive, reliable, and requiring no external power supply, are widely used for level measurement in various storage tanks and process vessels. However, it is common to encounter situations where the level gauge display does not change with the liquid level—the liquid level has clearly risen or fallen, but the level gauge column remains unmoved. The causes of this phenomenon can generally be summarized as follows:
1. Float Jamming or Failure
The float is the core component driving the level gauge's rotation. If the float becomes heavier due to scaling, crystallization, or viscous substances adhering to it, and gets stuck on the inner wall of the measuring tube, it will not rise or fall synchronously with the liquid level. Furthermore, demagnetization or corrosion of the internal magnet of the float, allowing media to enter the float, will also cause it to lose buoyancy or magnetism, rendering it completely inoperable. For media containing ferromagnetic impurities, these impurities are adsorbed onto the surface of the float or the inner wall of the measuring tube, similarly causing jamming.
2. Level Gauge Assembly Failure
The level gauge column relies on the magnetic coupling between a small internal magnet and the float to achieve rotation. After prolonged use, the small magnet may demagnetize, rendering it unable to be driven by the float's magnetic force. Corrosion, wear, or blockage of the flapper shaft can cause it to become sluggish, resulting in the flapper getting stuck on the red or white side and refusing to change direction. Some flappers use a two-color plastic sheet structure; prolonged exposure to sunlight can cause aging and deformation, making it difficult to flip.
III. Changes in Media Characteristics
When the actual medium density deviates significantly from the design value, the buoyancy force on the float is insufficient (medium density lower than design value) or excessive (density higher than design value causing the float to float too high), preventing the float from driving the flapper at the normal liquid level. When the medium viscosity is too high, the float's resistance to rising and falling increases, resulting in severe lag or even complete immobility. For easily vaporized media, insufficient heating can lead to vapor evaporation and air bubbles in the measuring tube, causing the float to jump or become stuck.
IV. Installation and Maintenance Issues
Excessive verticality of the level gauge installation, or significant misalignment between the upper and lower flanges and the container connecting pipes, can cause the float to deviate from the center and rub against the inner wall of the measuring tube. Long-term neglect of the drain valve can cause sediment buildup at the bottom, blocking the float and preventing it from descending. Additionally, if the flapper panel is too far from the measuring tube or is not installed parallel, the magnetic coupling strength will weaken, causing the flapper to malfunction.
V. Effects of Temperature and Pressure
Under high-temperature conditions, the magnet inside the float may irreversibly demagnetize, losing its driving force. At low temperatures or during rapid cooling, the medium may solidify or freeze, directly locking the float. Sudden pressure changes causing deformation of the measuring tube can also jam the float.
When a magnetic level gauge fails to respond to changes in liquid level, first check if the float is jammed or demagnetized. Then check the flexibility of the flapper shaft and the condition of the magnet. Simultaneously, verify that parameters such as medium density and viscosity are within the design range. Regularly cleaning the measuring tube, calibrating the float, and maintaining installation verticality can effectively prevent such malfunctions.
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