First is the mechanical reasons, usually having:
(L) the moving parts are not balanced. Apart from manufacture or welding of the rotor dynamic balance out particularly, localized corrosion and wear of the impeller or blockage may also cause loss of balance.
(2) dynamic and static parts of collision. This may be caused by bending the shaft, bearing wear or other reasons, or it may be due to the axial thrust balancing device failure, cause axial movement of the impeller touches the pump case.
(3) the pump base is not good. Such as bolts loosen, chassis stiffness and loss of resonance or pedestal sink with the pump axis.
(4) coupling on bad or improper piping installation lead to loss of pump shaft.
(5) vibration the motor itself, can be disengaged coupling operation check.
Second is the liquid causes may be:
Phenomenon of cavitation. This phenomenon caused by vibration and noise are usually produced in large, high frequency (600~25000HZ), you can see if the suction vacuum is too large to help determine. Can usually reduce the flow (such as turning down the discharge valve or reduced speed), reduce liquid temperature or increase the height readout method to eliminate.