According to the process of generating unbalance, it can be divided into initial unbalance, gradual unbalance and sudden unbalance.

Initial unbalance is caused by manufacturing deviation, assembly deviation and uneven material of rotor. If the dynamic balance does not reach the precision standard of dynamic balance when leaving the factory, it will cause great vibration at the beginning of use.

Progressive unevenness is caused by such factors as uneven scale on the rotor, uneven sediment of soot in the medium, uneven damage of particles in the medium to blades and impeller, and erosion of the rotor caused by working medium.

Its main manifestation is that the vibration value expands gradually with the extension of operating time.The sudden unevenness is caused by the parts on the rotor falling off or foreign matter sticking to the impeller runner or stuck plug, and the vibration value of the unit is stabilized at a certain level after the sudden obvious expansion.

According to its mechanism, imbalance can be divided into four categories: static imbalance, force couple imbalance, quasi-static imbalance and dynamic imbalance.