# New Hydraulic High-Pressure Impulse Generator for Long-Duration Impulse Tests
## 5 Experimental Results  
As shown in Figure 9a, the hydraulic system for the new hydraulic high-pressure impulse generator consists of an impulse generator designed considering all the parameters  
Figure 8: Evaluation of the unpredictable factors. (**a**) Effect of different values of the bulk modulus. (**b**) Effect of different volumes of the high-pressure chamber.  
listed in Tables 1 and 2, a gear pump and a relief valve to provide the input peak pressure, a flow-control valve to obtain a pressure drop, another relief valve to maintain the rated input pressure, and a pressurized tank to provide the back pressure. Two input pressure values are monitored by pressure gages, whereas the output pressure is observed and recorded by the pressure sensor which is set on the connector part as in Figure 9b. The sampling frequency of the output pressure is 100 Hz as considered the long-duration application. The details of critical hydraulic components are listed in Table 3.  
Before the start of the test, an exhaust procedure was performed, and the oil temperature was set at around 25 \({}^{\circ}\)C under constant room temperature and monitored by the temperature transducer on the tank. The motor was controlled to rotate at 30 rpm to obtain 1-Hz water hammer waves.  
Figure 10 illustrates the simulation results and the experimental data for one period. It is obvious to notice the good consistency between calculations and experiments except the rate of pressure rise. The experimental results indicate a higher rate, which is most likely caused by the unpredictable volume of the high-pressure chamber as shown in Figure 8b. Besides, although the whole experimental curve is within the limited area, the pressure peak is flat at the 150% rated pressure for a short time (around 10 ms). The most likely reason for this phenomenon is the 100 Hz sampling frequency is insufficient to obtain the real peak point of pressure. The results for randomly selected 10 continuous periods are shown in Figure 11. In this figure, it can be seen that the peak pressure points of all 10 waves is below 155% of rated pressure (25 Mpa), but there are two of them larger than 150% of rated pressure (25 Mpa). This also certifies the analysis result for the above flat pressure peak. However, the results in Figure 11 prove that this impulse generator can provide well-repeated water hammer waves until any component of the test rig fails.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Name** & **Description** \\ \hline \hline \multirow{2}{*}{Gear pump} & 20 Mpa rated pressure, 3 mL displacement, \\  & 2500 r/min rated rotational speed \\ \multirow{2}{*}{Relief valve} & Controllable pressure 0–20 Mpa \\ \multirow{2}{*}{Motor} & 1.5 kw, 1430 r/min \\  & Pressure sensor & Range 0–400 bar, accuracy \(\pm\) 0.3\% \\ \multirow{2}{*}{Hydraulic oil} & 45\# anti-wear hydraulic oil \\ \hline \hline \end{tabular}
\end{table}
Table 3: Details of the hydraulic components.  
Figure 9: Test rig of the new hydraulic high-pressure impulse generator. (**a**) Schematic of the hydraulic system for the test rig. (**b**) An overview of the test rig.