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API Plan 23

Forced circulation from the seal chamber through a cooler and back to the seal chamber.

API Plan 23


This plan involves the forced circulation of process fluids from the seal chamber through a seal flush heat exchanger and back to the seal chamber.

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Application Notes

  • Seal has an internal circulating device (pumping ring) that circulates seal chamber fluid through a cooler and back to the seal chamber.
  • Provides a cool flush to the seal to improve lubricity, reduce coking, and/or avoid fluid flashing to vapor.
  • Commonly used for hot water services above 180°F [80°C] (e.g. boiler feed water) and hot hydrocarbon services.
  • Throat bushing is used to isolate product in the seal chamber from product in the pump volute.
  • More energy efficient than Plan 21 since only the fluid in the seal chamber is run through the cooler.
  • If the cooler duty is high, fouling and clogging on the water side can occur over time.
  • Potential for clogging on the process side if the fluid becomes too viscous at reduced temperature.
  • Best piping practices must be followed to avoid vapor entrapment and stalled flow in the tubing.


  • Improved energy savings compared to Plan 21
  • Cool flush improves seal lubricity and reduces coking


  • The use of products with a high viscosity can negatively affect fluid circulation
  • Maintenance of the Seal Cooler although better than Plan 21

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