Factors Influencing the Vibrations of a Magnetically Suspended Pump

Vibrations are a common problem in pumps that reduce the pump efficiency, cause excessive noise, and can even induce fatigue failures. Active magnetic bearings (AMBs) have been extensively investigated to reduce vibrations. Most research has focused on control methods to reduce the vibrations, but the mechanical characteristics of the bearing are also important for vibration isolation since they are the main vibration transfer path. A finite element model of a 30 kW pump prototype suspended on 5-DOF AMBs was used to analyze the pump vibrations with the AMBs simplified to spring-dampers with equivalent stiffness and the damping related to the rotational speed. Two external excitations were analyzed with an unbalanced centrifugal force acting on the rotor in one case and the other case having a hydrodynamic force acting on the impeller. The model was simplified to improve the simulation efficiency by using a time dependent hydrodynamic force obtained from a CFD model that was assumed to not be affected by the system parameter changes. The model was then used to investigate the effects of several key structural parameters on the magnetic pump vibrations, including the motor shell thickness, the junction box position, the stiffness and damping of the magnetic bearing and the isolator as well as the mounting method. Then, the results were used to design a new pump with FE simulations used to judge the effectiveness of the design. The simulations show that the design effectively suppresses the vibrations at the working speed. This research provides a method for designing pumps with less vibrations.