API Plan 53B

API Plan 53B

Barrier fluid system pressurized by a bladder accumulator supplying clean liquid for an arrangement 3 pressurized dual seal.

A  Cooler
B  Bladder accumulator
C  Drain
D  Vent

Seal chamber details

4  Flush (F)
5  Liquid barrier OUT (LBO)
6  Liquid barrier IN (LBI)
7  Seal chamber

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

P&ID according to API


1  Make-up barrier liquid
2  Bladder accumulator
3  Bladder charge connection
8  Vent
9  Barrier fluid drain
10  Valve* (for checking accumulator bladder integrity)

PI  Pressure indicator*
PIT  Pressure transmitter with local indicator
TI  Temperature indicator**
TIT  Temperature transmitter local indicator

* If specified, both the PI and valve 10 shall be installed for checking bladder integrity.
** If specified.
*** Vertically oriented, finned air cooler shall be installed if specified




  • The barrier fluid and nitrogen are separated by a bladder which effectively prevents the nitrogen from mixing with the barrier fluid as in the case of a Plan 53A.
  • The pumped medium generally does not leak to the atmosphere unless the bladder pressure is lost.
  • High reliability as a stand-alone system without need for a permanent nitrogen source and external pressure.
  • Heat removal by water or air cooler.
  • Uses an internal circulating device to ensure barrier liquid circulation.
  • Barrier liquid enters the process medium through the inner seal faces.


  • 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 a permanent, reliable nitrogen supply at required pressure.
  • For applications with barrier pressures above 16 bar (232 PSI) where Plan 53A cannot be used.

Remarks, checkpoints

  • Check with the process engineer if product contamination is acceptable.
  • Check barrier fluid compatibility with the media.
  • Always pre-charge the bladder at the correct pressure to ensure the required barrier pressure at the operating temperature. Refer to the nameplate affixed to the accumulator.
  • Vent the system before start-up. Later ensure that the vent line always remains closed.
  • Sense the seal inlet and outlet line temperatures. Difference in the temperatures is an indication of proper flow.
  • Ensure that the barrier pressure is always higher than the seal chamber pressure by at least 1.4 bar (20 PSI).
  • Since there is less barrier fluid volume in the accumulator, heat dissipation is a function of the cooler efficiency.

Pump media characteristics

  • Suspended solids
  • Polymerizing and contaminated media
  • Poor lubrication properties
  • 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, flushing and cooling for both inboard as well as outboard seals.




API 682 4th Edition

Contact us

Follow the direct link to your API 682 4th ed. contact

Show locations

API piping plan tool

Download the free EagleBurgmann API piping plan tool and benefit from useful and practical information

PDF download - 4.0 MB

Excellence in Practice

With our free e-mail newsletter „Excellence in Practice“, you will receive first-hand information about current products, services, references and worthwhile industry insights.