API Plan 23

API Plan 23

Recirculation from a circulation device in the seal chamber through a cooler and back into the seal chamber.

A  Circulation device
B  Cooler
C  Temperature indicator
D  Vent
E  Drain

Seal chamber details

1  Flush outlet (FO)
2  Flush inlet (FI)
3  Quench (Q)
4  Drain (D)
5  Seal chamber

Example seal: EagleBurgmann SHF single pusher mechanical seal.

P&ID according to API


6  Vent (normally closed)
7  Drain (normally closed)
TI  Temperature indicator

* Vertically oriented finned air cooler shall be installed if specified.


  • Product in seal chamber is isolated from pumping area using a close clearance throat bushing.
  • Increases product temperature margin in the seal chamber thus avoiding vaporization.
  • Seal runs at a lower stabilized temperature of the media.
  • Removes only the generated seal face heat and the heat soak from the pump area, thus the cooler is smaller and more effective as compared to an equivalent Plan 21.
  • Uses a pumping ring for circulation in running condition.
  • In idle condition, thermosiphon effect ensures circulation.
  • A distributed flush is not recommended for this plan.


  • Hot hydrocarbons.
  • Hot water services above 80 °C (176 °F).
  • Boiler feed water.
  • Applications where increasing seal chamber pressure to improve vapor pressure margin is not possible.

Remarks, checkpoints

  • For media with high viscosities and higher freezing points, steam must be used in the cooling lines instead of water.
  • A high-point vent valve to be provided to vent the system before start-up.
  • A close clearance throat bushing must always be in place to reduce the heat soak from the pump.
  • Avoid sharp bends and 90° elbows in piping. Piping should be smooth and continuously rising.
  • Cooler to be installed approx. 500 mm (20 ”) above pump centerline.
  • Good quality cooling water is recommended to avoid deterioration of cooler efficiency.
  • Flush outlet from seal chamber should be in the top half of the seal gland plate or the seal chamber.

Pump media characteristics

  • High temperature, clean non-polymerizing fluids.
  • Close to vaporization point.

Location, function

  • Process side
  • Flushing and cooling




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