## 5 Verification Based on Leakage Signal in Check Valve  
In the initial stages of hydraulic valve leakage, the hydraulic circuit pressure remains relatively stable, making detection challenging when using conventional pressure sensors due to their installation and removal complexities. While acoustic emission sensors offer an alternative, their deployment requires precise coupling with the measurement surface to ensure optimal acoustic transmission, which presents operational difficulties. Additionally, acoustic emission signals, characterized by their ultra-high frequency nature, demand high sampling rates and generate large data volumes, consequently reducing the data-processing efficiency. Magnetic vibration sensors are easy to install and can capture low-frequency features in leakage signals. Therefore, this experiment collected the leakage vibration signals inside the valve as the research object. The check valve is an important hydraulic component that controls the flow direction of the fluid medium, and its wear has a great impact on the performance and efficiency of the hydraulic system. In this study, the SV10 PB1-30B hydraulic check valve produced by Huade Company was used as the experimental object. Based on three common types of valve leakage, namely permeation leakage, gap leakage, and jet leakage, this experiment configured three distinct fault conditions in the check valve: entire seal surface defect, local seal surface defect, and eccentric spool defect. These configurations were designed to simulate the actual leakage scenarios of check valves in engineering applications. The fault check valve element is shown in Figure 7. From left to right, this included an entire seal surface defect check valve, local seal surface defect check valve, and eccentric spool defect check valve. The experiment was carried out using an RCYCS-G hydraulic system failure test bench. The test bench is shown in Figure 8. The test bench consists of a load-lifting module, a control module, and a hydraulic circuit module where the tested check valve is located. Through the data acquisition system, the leakage vibration signals in the check valve of entire seal surface defect, local seal surface defect, and eccentric spool defect are collected. The data acquisition box model was NI PXI-1062Q, the data acquisition card model was NI PXI 4492, and the vibration accelerometer model was 1A111E. The sensor installation position is shown in Figure 9.  
Figure 6: Time-frequency diagram of output signal using CMSR. The experimental procedure was systematically conducted in three distinct phases: lifting, pressure holding, and falling. Prior to experimentation, calibrated weights were applied to the test bench to ensure that the check valve could sustain a predetermined load pressure during the pressure-holding phase. During the pressure-holding stage, the leakage signals in the check valve of three different fault types were collected at a sampling rate of 2000 Hz for a duration of 3 s. There were no other disturbances such as pressure holding, and the pressure holding phase. Figure 8: RCYCS-G hydraulic system fault test bench. Figure 7: Fault component of check valve. Figure 9: Sensor installation position. motor vibrations when the test bench was turned on during the pressure-holding phase, so the ambient background noise was low. To enhance the practical relevance of the experimental conditions, Gaussian white noise with an intensity of 0.0008 was introduced to the internal leakage signal, effectively obscuring the original signal and generating a noisy signal. Subsequently, these three preprocessed fault signals were processed through the SaRT-CMSR system for parameter optimization, yielding the corresponding system output signals. The spectral characteristics of each signal were then extracted through Fourier transform analysis.