856A2904G02 is a precision aerospace component, compliant with AS9100D quality standards and FAA/EASA regulations, designed for the hydraulic systems of large commercial aircraft, as a matching part for the 856A2904G01 hydraulic pressure relief valve.

It serves as an auxiliary seal ring for the hydraulic pressure relief valve, forming a secondary leak-proof seal between the valve's guide sleeve and valve body. This seal enhances the pressure control accuracy of the relief valve, preventing minor hydraulic fluid leakage that would reduce the valve's pressure regulation sensitivity, cause slow response to overpressure conditions, or lead to unnecessary pressure loss in the hydraulic system during normal flight operations.

Made from oil-resistant, high-pressure and high-temperature resistant fluorosilicone rubber, it operates stably at -45°C to 250°C, and resists long-term contact with aviation hydraulic fluids. Weighing 0.05kg, it allows fast MRO replacement, a key component for maintaining the hydraulic pressure relief valve's performance.