# Research on Prediction Method of Hydraulic Pump Remaining Useful Life Based on KPCA and JITL
## 4 Life-Cycle Test and Signal Acquisition of Gear Pump  
### Life-Cycle Signal Acquisition  
The test system used in this study is a gear pump accelerated life test bed. The pump outlet pressure was set to different stress levels in the test process, including 23 MPa, 25 MPa, and 27 MPa. The physical diagram of the test bed is shown in Figure 3. The test bed can load four hydraulic pumps at the same time and use pressure sensors to collect pressure signals at the outlet of hydraulic pumps. In order to prevent the damage of the hydraulic pump air suction, four pumps are arranged in turn on the lower side of the tank. The hydraulic system schematic of gear pump life-cycle test bed is shown in Figure 4. Each gear pump has two circuits of high and normal pressure. The pressure of relief valve 10.1-10.4 of the rated working pressure circuit is set to 20 MPa. The pressure of relief valve 10.5-10.8 of the high-pressure acceleration circuit is set to different stress levels. The relief valves 10.9-10.12 are safety valves. During the test, four gear pumps of the same model are operated simultaneously. A pressure sensor is installed at the pressure outlet of each gear pump. A total of four pressure sensors are installed based on the number of gear pumps. The models and performance parameters of the main components used in the test bed are listed in Table 3.  
Figure 4: Hydraulic system schematic of gear pump life-cycle test bed: 1—Tank; 2—Liquid thermometer; 3—Return oil filter; 4—Forced-air cooler; 5—Air filter; 6—Self suction oil filter; 7—Electric motor; 8—Gear pump; 9—High-pressure hose; 10—Relief valve; 11—Pressure gauge; 12—Flow meter; 13—Valve block; 14—Electromagnetic reversing valve; 15—High pressure filter; 16—Pressure sensor; 17—Torque-speed transducer; and 18—Temperature sensor. Figure 3: Life-cycle test bed of gear pump: (**a**) Topside of test bed and (**b**) Underside of test bed. The gear pump life-cycle test system is designed with four gear pumps, which are loaded simultaneously during operation. Each gear pump has two circuits of high and normal pressure. The high- and normal-pressure circuits are also called the high-pressure acceleration branch and the rated working pressure branch, respectively. The pressure of relief valve 10.5-10.8 of the high-pressure acceleration branch is set to different stress levels. The pressure of relief valve 10.1-10.4 of the rated working pressure branch is set to 20 MPa. In the actual operation of each gear pump, no flowmeter is installed on the high-pressure acceleration branch. When the gear pumps operate in the high-pressure acceleration branch for 59 min and 40 s, reversing valve 14 starts to work. Subsequently, the gear pumps operate in the rated pressure branch for 20 s, and the gear pump signals are collected in the last 2 s. The sampling frequency of the signal is set as 12 kHz. During the test, a data acquisition program written using LabVIEW is used to collect the vibration, pressure, and flow signals, of the gear pumps. The operation states of the gear pumps are monitored throughout their life cycle. In the gear pump stress loading, for the stress level, the method of pressure average deployment is used, by which the acceleration pressure is set at the lowest value of 23 MPa and the highest of 27 MPa. In the process of pump outlet pressure loading, the pressure of relief valve 10.5-10.8 is set to different stress levels, including 23 MPa, 25 MPa, and 27 MPa. The test method of the non-substitute time tac-tail life experiment is adopted [51; 52; 53]. After 300 h of operation at the first stress level (23 MPa), the stress level is increased to the second stress level (25 MPa), and after 300 h of continuous operation, the stress level is changed to the third stress level (27 MPa). A schematic of the step-stress acceleration degradation test is shown in Figure 5.  
During the life cycle test of the gear pumps, hazards such as a decrease in oil viscosity and an increase in leakage can be caused by a high oil temperature.