Rubber J-Bulb Seals Used for High Head Bulkhead on Corroded Surface

This paper describes the process used to design rubber J-bulb bulkhead seals used for dewatering at the San Francisco Public Utility Commission Hetch Hetchy Water & Power O’Shaughnessy Dam. Major design considerations included varying pressure conditions from 40 feet to nearly 300 feet of head on the seals and design of the seals for leakage control against corroded surfaces that had been underwater for over 100 years. While finite element modeling was used to predict seal displacement and stress at the varying loads, a laboratory test program was also designed and implemented to confirm conditions for seal deployment and to predict the magnitude of displacement that might be expected at varying head conditions. Details that will be discussed include seal profile and hardness, bearing/spacer bars, seal stem and bulb deflection and confinement, clamp bar compression to reduce leakage, flow required to initiate the seal, bearing surface preparation, and other details impacting seal effectiveness. The resulting design was successfully fabricated and field tested, and was proven to provide a manageably small amount of leakage under varying head conditions, even when sealing against a highly corroded surface. A companion paper presented at the 2025 ASDSO Conference describes the design of unique aspects of the steel bulkhead and lifting beam assembly.