What is surge in centrifugal fans?

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“\"Surge\" is an unstable operating condition that causes abnormal performance in centrifugal fans. When a centrifugal fan experiences surge, periodic oscillations in airflow occur throughout the entire fan and piping system. Moreover, a whistling noise similar to that of panting is produced, which **further increases the vibration of the entire unit. In severe cases, pressure imbalances can cause intense vibrations, leading to damage to seals and bearings, with serious consequences. Therefore, in actual production, efforts should be made to avoid operating the fan at the surge point; once it operates at this point, appropriate measures must be taken immediately to address the issue. 　　Once surge occurs in a centrifugal fan, the operating conditions of the unit and the piping system exhibit the following distinct characteristics: the outlet pressure and inlet flow rate of the gas medium change significantly, and sometimes gas backflow may also occur. When the gas medium is discharged by the fan and then flows back, it represents a relatively dangerous operating condition. The pipeline network experiences periodic oscillations with large amplitudes and low frequencies, accompanied by periodic \"roaring\" sounds. 　　The fan vibrates intensely; both the casing and bearings experience strong vibrations, along with a loud, periodic airflow noise. Due to the intense vibration, the liquid lubrication conditions of the bearings are disrupted, the bearing shells can be damaged, and even the shaft may break. Friction and collisions between the rotor and the stator occur, as well as severe damage to the sealing elements.