Multi-State Parameter Monitoring for Comprehensive Performance Evaluation of Hydraulic Reciprocating Seals: A Case Study of VL Combined Seals

During practical service, the interfaces of hydraulic reciprocating seals experience complex coupling interactions of lubrication, contact stress and thermal effects. Reliance solely on standard indicators including leakage rate and cycle count cannot capture latent interfacial risks originating from lubrication failure, contact overload and thermal accumulation under designated operating conditions, which greatly limits the evaluation and optimal selection of hydraulic reciprocating seal configurations for targeted service scenarios. This work presents a multi-state monitoring approach based on ultrasonic oil-film measurement and fiber Bragg grating contact-stress sensing, and constructs a multi-dimensional evaluation indicator system for seal-interface latent risks. Combined with an interface–risk-coupled weighting strategy, indicators such as oil-film thickness, contact stress and interface temperature are utilized to quantify seal-interface risks and enable comprehensive performance assessment and comparison among different seal configurations. Long-cycle comparative experiments were conducted on three VL combined-seal configurations at 2 MPa, 21 MPa and 35 MPa via a high-speed hydraulic reciprocating seal performance-test rig. The results show clear pressure-dependent adaptability: the 2.2 mm configuration achieved the highest closeness coefficient at 2 MPa (Ci=0.8176), whereas the 2.1 mm configuration ranked first at 21 and 35 MPa, with Ci=0.6992  and 0.9252, respectively. These results provide a quantitative basis for structural optimization and operating-condition-matched configuration selection.