API Plan 74

API Plan 74

Externally supplied barrier gas for arrangement 3 dual pressurized non-contacting gas seals.

A  Gas OUT
B  Gas IN

Seal chamber details

2  Vent (if required)
3  Gas barrier inlet (GBI)
4  Gas barrier outlet (GBO) (normally closed), used only to depressurize barrier
5  Seal chamber

Example seal: EagleBurgmann CGSH-KD dual pusher mechanical seal.

P&ID according to API


1  Barrier gas panel
3  Gas barrier inlet (GBI)
4  Gas barrier outlet (GBO) (normally closed), used only to depressurize barrier
6  From barrier gas supply

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


  • Nitrogen is used as barrier gas.
  • Pumped media never leaks to the atmosphere.
  • High reliability due to the absence of foreign particles/solids in the barrier gas.


  • For dual pressurized non-contacting seals.
  • For media with moderate temperatures, with poor lubrication properties or with hazardous or toxic nature.
  • For services where media contamination is acceptable but no media leakage to atmosphere is tolerated.
  • Flashing light hydrocarbons.

Remarks, checkpoints

  • Check if nitrogen is compatible with the pumped media.
  • Ensure that the barrier gas pressure is higher than the seal chamber pressure by at least 1.7 bar 25 PSI).
  • Set the back pressure regulator at least 1.7 bar (25 PSI) above the seal chamber pressure.
  • Check filter from time to time for any blockages.
  • Do not use for polymerizing and sticky media as this creates problems with the inboard seal faces.
  • Ensure a reliable nitrogen supply. Avoid usage of nitrogen gas bottles.
  • Use individual gas panel per seal assembly in a between bearing pump.

Pump media characteristics

  • Poor lubrication
  • Clean, non-polymerizing moderate temperature fluids.
  • Hazardous / environmentally harmful
  • Close to vaporization point
  • High vapor pressure media

Location, function

  • Between seals
  • Barrier system (psealchamber < pbetweenseals)