In practical operation, pump turbines typically operate far from their designed working points, which has a significant impact on the stability of the unit’s operation. In this paper, we conducted a field test to investigate the stability characteristics of prototype pump turbines at different working points. By adjusting the given power of the generator in a stepwise manner to control its working point, we obtained the statistical and spectral characteristics of pressure signals and acceleration signals. In turbine mode, the result shows that, at low, medium, and high power, the variation in pressure fluctuation characteristics is influenced by three different factors, while vibration generally reaches its maximum value at approximately 50 MW. In pump mode, variations in pressure were observed among different measurement points in the low-frequency range, and the characteristics of vibration acceleration were influenced by both the rotor–stator interaction (RSI) and the structural modal frequencies. We emphasized that the high-frequency bands have influences on the unit comparable in magnitude to those of the rotor–stator interaction, which has rarely been mentioned in previous studies. Through detailed testing and analysis of the unit’s actual operation, we can gain a better understanding of its behavior and performance in the turbine and pump modes, and these results hold significant importance for ensuring the stability and reliability of the unit.

The disk structure is widely used in hydraulic machinery such as turbine runners and pump impellers, with its vibration characteristics directly affecting operational stability and service life of equipment units. In this study, to better reveal the underlying mechanisms influencing disk vibration behaviour, an acoustic fluid-structure coupling model is established, aiming to investigate how variations in radial and axial wall distances affect the natural modes of disks in water. The findings demonstrate that as the size of gap decreases, the enhanced added mass effect leads to reduced natural frequencies, with the frequency reduction rate exhibiting a nonlinear growth trend. The influence of axial wall proximity is more significant, and the added mass coefficient gradually decreases with increasing nodal diameter number. These findings provide theoretical guidance for gap design and vibration optimization in hydraulic machinery.