**6. Conclusions**

Pressure fluctuation of hydraulic pump can be caused by the center spring wear fault, and the fault feature information of fluctuation is heavily influenced by fluid flow contamination. Aiming to resolve this problem, Autogram is applied to extract the fault feature information from the fluid pressure signal. The research results indicate that standard Autogram can extract more fault feature information on center spring wear than upper Autogram and lower Autogram, especially standard Autogram based on no threshold processing. Autogram also performs better than FK in extracting the fault feature information.

**Author Contributions:** Conceptualization, Z.Z.; Methodology, Z.Z.; Investigation, Z.Z. and X.L.; Writing-Original Draft Preparation, Z.Z.; Writing-Review and Editing, Y.Z. and Z.Z.

**Funding:** This research was funded by the Startup Foundation for the Doctors of North China University of Science and Technology (0088/28412499), the National Natural Science Foundation of China (51805214), and the China Postdoctoral Science Foundation (2019M651722).

**Conflicts of Interest:** The authors declare no conflict of interest.
