Transient thermo-elastohydrodynamic model and tribology characteristics of combination seals in piston pump conditions

The combination seal is widely used in the high-speed and high-pressure applications involving of reciprocating seals. There is the limited publicly available information on its sealing performance under the piston pump conditions that the seal pressure and reciprocating velocity are periodic variations. Unfortunately, test results indicate that the seal failed within a short time, despite the pressure and reciprocating speed meeting existing standards, and the failure mechanism remains unclear. A novel transient thermo-elastohydrodynamic model and analysis scheme of the combination seal, considering the time-varying seal pressure and rod velocity, are established. The model gains insight into the transient sealing characteristics, encompassing contact, heat transfer, friction, and fluid transport. It accurately predicts the time-varying friction force corresponding to the experimental results, and some attractive findings are obtained. The temperature rise of the seal and film under high water-based medium conditions is limited; with a maximum temperature rise of 5.68 K. A greater frequency of pressure and velocity variation results in smaller leakage but greater wear, caused by the increased contact pressure, which is the main form of failure. The time-scale effect of film-squeezing effect and viscoelastic relaxation are the main reasons for the significant increase in contact pressure with variation in frequency. The influence of pressure variation on fluid pressure and contact pressure is more sensitive than that of the reciprocating velocity. The frequency of pressure variation must be considered in seal design and relevant standards; otherwise, serious wear will occur.