API Plan 53A

API Plan 53A

Pressurized barrier fluid reservoir supplying clean fluid for an arrangement 3 pressurized dual seal.

A  From mechanical seal
B  To mechanical seal
C  Filling connection
D  Cooling water IN
E  Cooling water OUT
F  Drain
G  From external pressure source

Seal chamber details

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

Example seal: EagleBurgmann LY9DZTT dual pusher mechanical seal.

P&ID according to API


1  From external pressure source
2  Reservoir
3  Make-up barrier liquid
7  Cooling water IN
8  Reservoir barrier fluid drain
9  Cooling water OUT
10  Barrier fluid drain

LI  Level indicator
LIT  Level transmitter with local indicator
PIT  Pressure transmitter with local indicator



  • The pumped media never leaks to the atmosphere unless the reservoir pressure is lost.
  • A nitrogen source is required for pressurization.
  • Provision of cooling coil inside the reservoir or an external water or air cooler takes care of the heat removal.
  • 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 lubricating the inner seal faces.
  • For barrier pressures up to16 bar (232 PSI).

Remarks, checkpoints

  • Always ensure that the source pressure is higher than the desired barrier pressure.
  • 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.
  • Decrease in the reservoir level is an indication of inboard or/and outboard seal leakage.
  • Ensure that the barrier pressure is always higher than the seal chamber pressure by at least 1.4 bar (20 PSI).
  • For barrier pressures above 16 bar (232 PSI) use Plan 53B, 53C or 54.
  • Check with the process engineer if product contamination is acceptable.
  • Ensure the compatibility of barrier liquid with the pump media.

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.