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API Plan 66A

Throttle bushings in the seal gland minimize the leakage leaving the seal gland and allows for detection of a seal failure.

API Plan 66A


This plan incorporates throttle bushings in the seal glands that reduce leaking and also enables rapid detection of seal failure.

Application Notes

  • Intended for use in Arrangement 1 applications where it is required to limit leakage in case of a seal failure or it is required to monitor excessive leakage.
  • Leakage out of the drain port is collected and piped to a liquid recovery system or sump.
  • As the leakage rate increases, the pressure will increase on the upstream side of the inner bushing which is in line with the pressure transmitter.
  • Pressure in the drain cavity will be monitored by the pressure transmitter and can be used to monitor seal performance and trigger an alarm.


  • Drain cavity pressure can be used to monitor seal performance


  • The use of inappropriate process fluids may cause obstructions at inner bushings

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