Optimal experiment and analysis on installation position for diffuser of centrifugal pump based on operating stability

Abstract: The hydraulic performances, pressure pulsations and vibrations of a single-stage single-suction centrifugal pump with radial diffuser at 3 different installation positions were tested for the purpose of improving the operating stability and exploring the best installation position. The experiment was conducted in a closed test platform. Numerical simulations were taken to find 3 typical positions. Through the simulation performance curve, the obvious difference occurred in 3 positions, i.e. the positions with the angle between volute tongue and radical diffuser blade of 0°, 20° and 40°. In order to provide 3 different positions, a unique radial diffuser with many positioning holes was made. Through changing the installation position of radial diffuser, 3 different testing pumps were obtained. The test measured the hydraulic performance of the pump, the pressure pulsation of the volute outlet section and the vibrations of the whole pump. The flow was measured by the turbine flow meter. The head and the power were calculated with the data gotten by the pressure transmitters in the inlet and outlet and the torque meter respectively. The pressure pulsation of the volute outlet section was measured by a high-frequency pressure transmitter. The vibration sensors were arranged in the pump, with 2 sensors monitoring the x direction and y direction respectively in the pump cover and 1 sensor monitoring the z direction in the bearing body. All the data were collected simultaneously. The sampling frequency was 10.24 kHz and the sampling time was 30 s. Through testing the pumps with 3 different radial diffuser installation positions, the data of the pressure and vibration acceleration were obtained, the performance curves, pressure pulsation amplitude, pressure pulsation characteristics in time domain and frequency domain, and the vibration amplitude and vibration characteristics in frequency domain were analyzed. The experimental results showed that when the volute tongue was set at the middle of the radial diffuser channel, the hydraulic performance of the pump was the best among all positions, and the maximum efficiency was higher by 2%. The vibration acceleration amplitudes at 3 different directions kept low value. However, the pressure pulsation amplitude would rise especially in the large flow, which was 2.25 kPa higher than other positions. Because of the existence of the radial diffuser, the blade passing frequency was not the main activating frequency, the 2 times and 3 times shaft frequency were the main activating frequency for the pressure pulsation, and the 2 times and 6 times shaft frequency were the main activating frequency for the vibration acceleration. With the flow increasing, the pressure pulsation amplitudes at volute diffuser section decreased firstly, reached the bottom under the 0.6 times designed working condition, and then increased. Different installation positions had slight effects on the pressure pulsation characteristics and vibration pulsation characteristics. The frequency law of the pressure pulsation and the frequency spectrum of the vibration acceleration kept almost the same under the same operating conditions. Therefore, the study provides a certain reference for the installation of the radial diffuser.