# Research on Fault Detection and Automatic Diagnosis Technology of Water Hammer in Centrifugal Pump
## 5 Test and Experiment
### Analysis of Results  
The waveforms of the original signal and filtered signal at measurement points 1 and 2 of the centrifugal pump under normal conditions and water hammer failure are shown in Figure 9. When no water hammer fault occurred, the original signal and filtered signal waveforms of measurement points 1 and 2 showed relatively stable characteristics, and there were no obvious impact signals. At this point, the kurtosis index, pulse index and margin index values of measurement points 1 and 2 were also relatively small. However, when a water hammer failure occurred, it can be observed from Figure 9 that there were impulse components present in both the original signal and filtered signal waveforms of measurement points 1 and 2. The kurtosis index, pulse index and margin index calculated during the experimental process are shown in Table 1. It can be seen that the original signal's kurtosis index, pulse index and margin index of measurement point 1 without water hammer failure were 2.10, 3.18 and 3.58, respectively, whereas the original  
Figure 8: Field experiment photos of centrifugal pump (measuring point 2). signal's kurtosis index, pulse index and margin index of measurement point 2 without water hammer failure were 2.57, 3.72, and 4.34, respectively. In contrast, the original signal's kurtosis index, pulse index and margin index of measuring points 1 and 2 significantly increased when a water hammer fault occurred. For example, the original signal's kurtosis index, pulse index and margin index of measurement point 1 increased to 2.49, 4.91 and 5.52, respectively, when a water hammer fault occurred, whereas the original signal's kurtosis index, pulse index and margin index of measurement point 2 increased to 4.86, 6.25 and 7.66 under the same conditions. It can be seen that the original signal's kurtosis index, pulse index and margin index of measuring points 1 and 2 underwent significant changes compared to the normal state when a water hammer fault occurred, increasing 1.19 to 1.54 times and 1.89 to 1.76 times, respectively. Compared with the unfiltered original signal, the index change in the filtered signal was more significant when a water hammer fault occurred. From Table 1, the kurtosis \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Measuring Point 1**} & \multicolumn{3}{c}{**Measuring Point 2**} \\ \cline{2-7}
**Parameter** & **Kurtosis** & **Pulse** & **Margin** & **Kurtosis** & **Pulse** & **Margin** \\  & **Index** & **Index** & **Index** & **Index** & **Index** & **Index** \\ \hline Original signal without & & & & & & \\ water hammer failure & 2.10 & 3.18 & 3.58 & 2.57 & 3.72 & 4.34 \\ Original signal with water & & & & & & \\ hammer failure & 2.49 & 4.91 & 5.52 & 4.86 & 6.25 & 7.66 \\ Multiple & 1.19 & 1.54 & 1.54 & 1.89 & 1.68 & 1.76 \\ Filtered signal without & & & & & & \\ water hammer failure & 3.12 & 5.09 & 6.00 & 2.91 & 4.61 & 5.44 \\ Filtered signal with water & & & & & & \\ hammer failure & 12.18 & 11.70 & 14.40 & 7.61 & 9.54 & 11.79 \\ Multiple & 3.90 & 2.30 & 2.40 & 2.64 & 2.07 & 2.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of time domain characteristics of the original and filtered signals at measuring points 1 and 2 under normal and water hammer conditions. Figure 9: Waveforms of original signals and filtered signals at measuring points 1 and 2 under normal and water hammer fault conditions. index, pulse index and margin index of the filtered signal at measurement points 1 and 2 increased 3.90 to 2.40 times and 2.64 to 2.18 times, respectively, compared to the normal state when a water hammer fault occurred. The multiples of the three indicators (kurtosis, pulse, and margin) were used with the corresponding indicators under normal conditions as the judgment criteria. If all three indicators exceeded twice the normal conditions, it was judged that a water hammer failure had occurred.