API Plan 51

API Plan 51

Reservoir providing a dead-ended blanket for fluid to the quench connection of the gland plate. Only recommended for vertical pumps.

A  Reservoir

Seal chamber details

1  From reservoir
2  Quench (Q)
3  Drain (D), plugged
4  Flush (F)
5  Seal chamber

Example seal: EagleBurgmann LL9UC single pusher mechanical seal.

P&ID according to API


  • Typically uses an auxiliary sealing device.
  • Can help to prevent icing on the atmospheric side.


  • Vertical pumps with dead-ended atmospheric quench


Remarks, checkpoints

  • Routine inspection of the liquid level is recommended.


Pump media characteristics

  • Tendency to ice at ambient temperatures.

Location, function

  • Atmospheric side
  • Quenching




* Remark: The configurations listed for each individual piping plan are to be understood as recommendations including possible utilizations which may also be applied.