Leakage mechanism analysis of electsro-hydraulic servo valve under transverse vibration environment

•Leakage of servo valve under transverse vibration is studied.•The contact pressure distribution model between threaded plug and servo valve considering thread profile angle and lead helix angle is established.•Threaded plug loosening dynamics model is established.•Experiments verify the method proposed in this study to evaluate the loosening of servo valve threaded plug. Electro-hydraulic servo valve is critical control element of hydraulic system in high-end aerospace equipment and operates in prolonged vibration environment. Due to airframe vibration and hydraulic shock, the servo valve is prone to leakage at the sealing end cap, leading to performance degradation and even failure. In this paper, an experimental analysis of servo valve leakage under transverse vibration is conducted, and the mapping relationship between threaded plug loosening and servo valve leakage is investigated. A dynamic model based on the contact pressure distribution between the servo valve and the threaded plug is proposed, and the leakage mechanism of the servo valve is examined from a dynamic perspective. The effects of hydraulic shock and sealing friction on plug loosening are explored, along with the influence of initial preload, vibration frequency, and vibration amplitude on plug preload decay. The results show that the preload decay of the threaded plug under transverse vibration is the primary cause of servo valve leakage, and this decay can be divided into two phases: a nonlinear rapid decline phase and a near-linear steady decline phase, which are influenced by transverse vibration and sealing friction, respectively. In summary, this study provides a valuable theoretical reference for understanding the leakage mechanism of electro-hydraulic servo valves.