1. centrifugal fan overspeed or overloading operation;
2. bad lubrication, or have scaling, damage and other phenomena;
3. the line point is close to the critical point, or falls into the critical speed region;
4. the actual value of the process parameters is deviated from the design value, such as temperature, flow rate, pressure and load, so that the fan can not operate normally.
www.jnblower.com