Fundamentals and Common Problems of Seal Integrity Robustness of Standardized Brake Tubing Threaded Connectors

There currently are only two industry wide utilized designs of standardized threaded connector for brake tubing. The ISO design incorporates a “bubble” style of tube's end-form while the JASO/SAE design includes double inverted “funnel” tube's flare. Both designs are based on the arrangement of two conical (frustum) surfaces which have to be pressed against each other in order to provide sealing. Seal integrity robustness of those standardized connectors is not sufficient as some retorquing is usually required in the course of the assembly process in order to seal a number of them. Accordingly each plant must allocate resources for the associated detection and rework process as they strive for zero leaks in the field. Numerous investigations and root cause analyses reveal some fundamental shortcomings in their sealing capability. In order to achieve sealed state of the connector some self-adjustment and certain degree of sustained deformation of its components is expected. In reality, excessive connector components variations and assembly process disturbances may impede connector's capability to overlap reasonable deviations. Consequently, reasonable torque increase may become not sufficient to seal the connector leading to deterioration of its actual level of seal integrity robustness. The article discusses the requirements, conditions and limitations of connectors' capability to achieve their sealed state. Sealing capability estimation based on torque control is contemplated. Some particular cases of no-seal condition despite torque increase are analyzed (a locked misalignment conditions, a “lift-off” phenomenon etc). The paper contains a discussion regarding improvement of connectors' sealing performance with respect to the assembly process via perfection of the design and current standards.