Experimental investigation of a self-adjusting piston sealing system coupled with a GRE hydraulic cylinder barrel for high-load and long-stroke applications

The rapid expansion of wind energy has highlighted the need for adaptive structural solutions to mitigate the visual and environmental impact of traditional fixed towers. This study presents the experimental validation of an innovative hydraulic lifting system designed for retractable wind towers. The proposed architecture overcomes the traditional manufacturing constraints of long-stroke metallic actuators by integrating a Glass Reinforced Polymer Epoxy (GRE) cylinder barrel with a novel radially self-adjusting piston sealing system. The cylinder barrel was constructed through the field-joining of standard commercial filament-wound pipes using an interlocking profile and external glass-fiber overwrap. To ensure hydraulic tightness despite the potential ovalization and geometric tolerances of composite structures, a specialized sealing assembly was developed. This system utilizes a double quad-ring configuration mounted on a self-adjusting Polytetrafluoroethylene graphite reinforced backup ring, designed to maintain continuous contact pressure against the internal resin surface of the GRE barrel. Experimental validation was conducted on a full-scale (1:1) test rig under a representative load of 200 kN. The system underwent 515 lifting cycles, simulating approximately one year of operational life, including over 1000 crossings of the pipe joints. Results demonstrated stable performance with no observed leakage or significative wear of the sealing elements.