What is the primary function of the sleeve on a flared-tube fitting?

The primary function of the sleeve on a flared-tube fitting is to help form a seal with the male fitting. When the fitting is assembled, the sleeve compresses the flared end of the tube against the male fitting, creating a tight seal that prevents fluid leaks. This sealing action is crucial for maintaining the integrity of the hydraulic or fuel systems in an aircraft, ensuring that fluids do not escape and that pressure is maintained.

The sleeve's design and fit facilitate proper alignment and sealing of the flared end to the male fitting surface, which is essential for safe and efficient operation in aviation systems. A properly seated and compressed sleeve contributes significantly to the overall reliability of the connection, making it an integral part of flared-tube fittings.