API Plan 53A is a pressurized seal support system designed for dual pressurized seals, ensuring zero process leakage by utilizing a barrier fluid at a pressure higher than the sealed process fluid. A standalone reservoir maintains this pressure through a nitrogen blanket or gas charging, allowing the barrier fluid to flow between the inboard and outboard seal faces via natural or forced circulation.

The higher-pressure barrier fluid prevents process fluid from escaping, making Plan 53A ideal for hazardous, toxic, or volatile fluids where zero leakage is essential. This system also improves seal cooling, reduces wear, and provides a reliable monitoring mechanism through pressure gauges and level indicators.