Experimental study on the unsteady performance of the multistage centrifugal pump

To improve the stability of the multistage centrifugal pump, a special test bench was built based on the Bently ADRE 408 portable vibration tester. Taking a cantilever multistage centrifugal pump as the research object, the axis orbit and the vibration spectrum of the pump were obtained at 0Qd (zero flow point), 1.0Qd (design flow point) and 1.5Qd (large flow point). Moreover, based on the Butterworth filter of the original axis orbit, we derived the axis orbit curve and the displacement time-domain diagram with fault information under different frequency multiplication, and also deeply studied the rules of vibration characteristics changing with different operating conditions and with different series at each monitor location. The results show that the axis orbit at the zero flow point is unstable and the vibration velocity is the highest which is caused by the imbalance of the mass; the axis orbit at the large flow point is stable and the amplitude of the vibration velocity is the smallest; the axis orbit of the design flow point is the most stable and the amplitude of the vibration velocity is the smallest. The maximum axis orbit displacements in the three operating conditions are all smaller than the unilateral space between the impeller and the diffuser, which avoids the radial friction between the rotor components and the static components. The axis orbit after the filter indicates that the rotor part has an unbalanced mass, and there is a fit clearance between the inner bore and the shaft diameter of the impeller, which can easily lead to the misalignment. Under different flow operating conditions, the blade frequency and its frequency multiplication are the main excitation frequencies of the multistage centrifugal pump, and to the pump casings at every stage, the main vibration frequency is one time and two times the blade frequency. This experimental study provides a new method to improve the stability and restrain the instability of the multistage centrifugal pumps.