API Plan 54

API Plan 54

Pressurized external barrier fluid system supplying clean liquid for an arrangement 3 pressurized dual seal. The barrier liquid is maintained at a pressure greater than seal chamber pressure and is circulated by an external pump or pressure system.

A  From external source
B  To external source

Seal chamber details

1  From external source
2  To external source
3  Flush (F)
4  Liquid barrier OUT (LBO)
5  Liquid barrier IN (LBI)
6  Seal chamber

Example seal: EagleBurgmann H75A4-B dual pusher mechanical seal.

P&ID according to API


1  From external source
2  To external source



  • Most reliable of all dual pressurized plans when properly engineered.
  • Provides barrier liquid circulation and cooling even though the process pump is in stand-by mode.
  • The pumped fluid becomes contaminated but never leaks to the atmosphere unless the system pressure is lost.
  • Ensures positive barrier fluid circulation and better heat dissipation due to higher flow rates as compared to 53A, 53B or 53C. Heat is removed with the help of a water cooler or an air cooler.
  • Uses a pump to ensure barrier liquid circulation and pressurization.
  • May employ a nitrogen / inert gas blanket for barrier oil applications.


  • Applications which require higher heat dissipation, which limits the use of Plans 53A, 53B, or 53C.
  • For services where product dilution is acceptable.
  • For services where media is unsuitable for flushing the inner seal faces.
  • For services where Plan 53A cannot be used due to non-availability of central pressure source.
  • For applications with high pressure and/or high temperature or where an internal circulating device would not lead to effective circulation.
  • Where a single system is utilized for multiple seals.


Remarks, checkpoints

  • Check with the process engineer if product contamination is acceptable.
  • Check barrier fluid compatibility with the media.
  • In case the system has a strainer or a filter, check for blockages.
  • Note that the loss of pressure in the system may cause the pumped media to enter the entire Plan 54 system.
  • Ensure that the barrier pressure is always higher than the seal chamber pressure by at least 1.4 bar (20 PSI).
  • Plan 54 systems need careful engineering based on the application.




Pump media characteristics

  • Suspended solids
  • Polymerizing and contaminated media
  • Poor lubrication properties
  • Hot services
  • Hazardous / environmentally harmful
  • Leakage may form solids
  • Close to vaporization point
  • Can tolerate dilution with barrier media

Location, function

  • Between seals
  • Barrier system (psealchamber < pbetweenseals)
  • Lubrication and flushing for the outboard seal and cooling for inboard as well as outboard seals.




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