When a centrifugal fan experiences surge, it can cause strong vibrations in the equipment, which not only affects normal operation but also significantly increases the likelihood of component damage. Therefore, it is necessary to take effective measures to prevent surge vibrations.
Fan Selection
When purchasing a fan, try to avoid a performance curve with a saddle shape, i.e., a curve that lacks a left lower corner. Surge typically occurs in this section of the performance curve. Even if only a right lower corner performance curve is available, try to shift the peak K of the performance curve to the left, meaning the flow rate Q(K) at the pressure peak should be as small as possible. Alternatively, ensure that the lower left section of the performance curve is as flat as possible to help prevent surge.
Install Exhaust Valve
To ensure the gas pressure in the fan is greater than the surge flow rate, an exhaust valve can be installed in the fan’s exhaust pipe. Some of the gas (Qb) is discharged, and the remaining part (Qc) is transported to the pipeline network (this flow can be below the surge flow rate).
This method is a simple anti-surge vibration technique, widely used in fans. Its disadvantage is that part of the energy gas is discharged through the fan impeller, which reduces the efficiency of the equipment.
Move Surge Boundary to Small Flow Zone
During installation and operation, change the fan’s speed, adjust the installation angle of the inlet guide vanes, or adjust the blades of an axial fan to move the performance curve to the small flow zone. The surge boundary will also shift to the small flow area, thus increasing the stable operating range of the fan.
Two-Valve Operation
Set two valves on the fan’s exhaust pipe, with the capacity between the two valves fixed to a certain value. The capacity between the two valves is equivalent to a gas reservoir. The first valve is directly installed near the centrifugal fan outlet and serves as a throttling valve. A slight throttling can prevent surge vibration. The second valve, further from the fan outlet, acts as a resistance. In practice, this setup not only stabilizes the system but also helps reduce noise.
To stabilize the operation of the entire system, it is best to select short pipes and install gate valves and nozzles for measuring flow. Dust filters should be placed as close as possible to the fan. A system with low pipeline resistance is less likely to cause surge in a short time.
Additionally, during daily maintenance, controlling the inlet guide vanes, managing the motor’s high current values, and regularly checking instruments can help prevent and reduce surge.