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API Plan 74

Externally supplied barrier gas maintained at a pressure greater than the seal chamber pressure.

API Plan 74


Plan 74 uses a buffer gas such as nitrogen in a dual seal system regulated by a control panel which allows the removal of moisture, gas filtration and barrier pressure regulation.

Application Notes

  • Used in Arrangement 3 dual pressurized seals, where the barrier medium is a gas.
  • Most common barrier gas is nitrogen. Ensure a reliable supply and avoid the use of bottles if possible.
  • Barrier gas must be pressurized prior to filling the pump and this pressure must be maintained at all times, including during standby.
  • Used with non-contacting and contacting mechanical seal solutions.
  • Typically used in applications that may contain toxic or hazardous materials whose leakage cannot be tolerated.
  • Barrier-fluid leakage to atmosphere is an inert gas (e.g. N2). Drainage and cleanup is not an issue as with dual liquid systems.
  • Inert barrier gas can be easily separated from the process stream.
  • Not recommended for services where sticky or polymerizing agents will be in direct contact with the seal faces; similarly, avoid applications that may lead to solids buildup.


  • Low installation and maintenance costs
  • Better safety profile as buffer gas leakage is inert


  • Discouraged in applications using polymerizing agents

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