## 3 Dynamic Prediction of Servo Valve Performance Degradation
### Servo Valve Erosion and Wear Test
#### 3.1.1 Test Hardware Configuration  
A schematic diagram of the servo valve spool erosion and wear test system is shown in Figure 2 below. The hydraulic pump 2 is the main pump for the entire flow control system and supplies the working medium or hydraulic oil. Thermometer 3 monitors the initial temperature of the hydraulic fluid and allows changes in the fluid temperature to be monitored at any time during the experiment. Two filters, 4 (1) and 4 (2), are used to filter large-diameter solid particles from the oil circuit. The main function of relief valve 5 is to regulate and maintain a constant pressure throughout the hydraulic system, so its main object of work is the source of the supplied fluid--the hydraulic pump 2. In addition, the four pressure gauges 6 (1)-6 (4) are used to check the pressure at the four oil ports of the servo valve and are connected to a pressure sensor that transmits the pressure signal to the computer. The throttle 8 regulates the system oil flow according to the experimental situation and can also be seen as a specific load acting on the servo valve of the measured flow. Finally, the two shut-off valves 9 can assume the on-off status of the servo valve's return port for the measured flow. When 9 (1) pathway and 9 (2) disconnect, representing the normal working fluid state of the experiment, that is, the measured flow servo valve erosion and wear experiments are constantly carried out. When the flow servo valve 7 is in the neutral position, 9 (1) is disconnected and 9 (2) is open, the flow meter 10 can be used to detect the zero leakage of the flow servo valve, and the flow meter can be connected to the flow sensor so that the leakage signal can be input to the computer. Figure 3 below shows the spool sleeve wear test rig, which includes a pump source, servo valve, flow meter, throttle valve, globe valve, heat exchanger, pressure gauge, thermometer, and associated piping system. (1) Hydraulic pump source: the hydraulic pump source used in this test has a rated pressure of 20.6 MPa and a rated flow rate of 100 L/min. (2) Servo valve under test: the servo valve used in this experiment has a maximum flow rate of 30 L/min. Figure 3: Spool valve sleeve wear test rig. Figure 2: Schematic diagram of the servo valve erosion and wear test system: 1—oil tank; 2—hydraulic pump; 3—thermometer; 4—filter; 5—relief valve; 6—pressure gauge; 7—direct-drive electro-hydraulic flow servo valve under test; 8—throttle valve; 9—shut-off valve; 10—flow meter. (3) Flowmeter: according to the rated flow rate of the system and the requirements of the pipeline system, this experiment used the model LWGYB-25 turbine flowmeter, with a range of 1 to 30 m\({}^{3}\)/h and an accuracy level of \(\pm\)0.5. (4) Throttle valve: in this experiment, throttle valve is equivalent to a flow control valve, and its requirements are low, so this experiment used the Shandong Taifeng hydraulic production model DVP-12 throttle valve. (5) Globe valve: according to the function of the globe valve in this experiment and the requirements of the pipeline system, we chose the model CJZQ-H20L ball core globe valve, whose nominal pressure is 20.6 MPa and nominal diameter is 20 mm. (6) Cooler: the test system was used in the BR005 type plate radiator; its design pressure is 1.3 MPa, and the design temperature is 150 \({}^{\circ}\)C, with heat transfer area of 6 m\({}^{2}\). (7) Pressure gauge: The pressure gauge used in this experiment is a shock-resistant pressure gauge, and the accuracy level of the pressure gauge is 1.6, where the range of the pressure gauge at the P, A, and B ports is 0 to 30 MPa and the range of the pressure gauge at the T port is 0 to 2.5 MPa. The pressure sensor was placed and connected in the pressure gauge. This test considered that the pressure gain and leakage changes are caused by the erosion and wear of particles on it, so this experiment adopted the method of real-time recording of pressure gain and leakage changes by the sensor incoming signal computer.