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.