API Plan 72

API Plan 72

Externally supplied buffer gas for arrangement 2 unpressurized seals with a dry running containment seal. Buffer gas is maintained at a pressure less than seal chamber pressure.

A  Gas OUT
B  Gas IN

Seal chamber details

2  Flush (F)
3  Containment seal vent (CSV)
4  Containment seal drain (CSD)
5  Gas buffer inlet (GBI)
6  Seal chamber

Example seal: EagleBurgmann H75LG4-C dual pusher mechanical seal.

P&ID according to API


1  Buffer gas panel
3  Containment seal vent (CSV)
4  Containment seal drain (CSD)
7  From buffer gas supply

FIL  Coalescing filter
FIT  Flow transmitter with local indicator
PCV  Pressure control valve
PIT  Pressure transmitter with local indicator


  • Is used together with Plan 75 (for condensing leakage) or Plan 76 (for vaporizing leakage).
  • The buffer gas is usually nitrogen and acts as a supply medium for the outboard seal and as a sweeping medium for leakages from the inboard seal.
  • Nitrogen blanket reduces the explosion hazard arising out of leakages from the inboard seal as well as prevents icing in cryogenic applications.


  • May be used for flashing as well as non-flashing services.

Remarks, checkpoints

  • Always ensure that the buffer gas pressure is less than the seal chamber pressure.
  • Set the forward pressure regulator to min 0.4 bar (5 PSI) above the normal flare pressure.
  • The buffer gas pressure should not exceed 0.7 bar (10 PSI).
  • Ensure that the CSV port is oriented to the 12 o'clock position and CSD to the 6 o'clock position.



Pump media characteristics

  • Hazardous / environmentally harmful
  • High vapor pressure fluids
  • Clean non-polymerizing fluids
  • Fluids condensing or vaporizing at ambient temperatures.

Location, function

  • Between seals
  • Buffer system (psealchamber > pbetweenseals)