API Plan 53B is a pressurized barrier fluid system that ensures zero process leakage in dual pressurized mechanical seals by utilizing a bladder accumulator to maintain the required barrier pressure. Unlike Plan 53A, where the pressure is maintained by nitrogen or gas charging, Plan 53B uses a flexible bladder to separate the pressurizing gas from the barrier fluid, preventing direct gas absorption into the fluid.

This design eliminates issues like gas entrainment and foaming, ensuring a more stable and reliable seal environment. Plan 53B is ideal for high-pressure and hazardous process fluids, offering enhanced cooling, lubrication, and monitoring through temperature and pressure controls.