Steam drum water level change is not caused by the damage of material balance relationship between the water supply volume and water evaporation volume, but due to suddenly changing of the working medium pressure or the suddenly changing of combustion condition, the bubbles in the water volume RGL bubble content increase or decrease,  so the  working medium volume will expand or shrink, which is referred to as a false water level.
1. During sudden change in load, the faster the changing speed of the load is, the more obvious the false water level has.
2. In case of steam turbine load rejection.
3. In the operation, the burning suddenly increase or decrease,  thus causing sudden increasing or reducing  of the quantity of bubbles, the water level instantaneously  rises or falls.
4. When safety valve is popping, the water level will  instantaneous rise obviously due to the pressure drop suddenly.
5. Due to the sudden stop burning of the boiler, the bubbles in boiler water will suddenly decrease and the water level will instantaneous decrease because the combustion is suddenly stopped. In case there is obviously changing of water level, the cause of the change and change tendency shall be analyzed to determine whether the false water level or the steam drum water level is really changed, it is required to timely and properly adjust water level. Improper handling will cause water shortages or overflow accidents.（lsh）