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API Plan 66B

An orifice plug in the drain port minimizes the seal leakage leaving the seal gland and allows for detection of a seal failure.

API Plan 66B


This plan is intended for use in Arrangement 1 seals where limiting leakage is critical to preventing seal failure. Plan 66B uses an outlet orifice plug in its drain port to limit seal leakage and detect seal failures.

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.
  • Replaces one of the bushings from Plan 66A with an orifice in the drain connection.
  • 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 orifice plug. An orifice plug is used to limit the amount of leakage out of the seal gland.
  • Pressure in the drain cavity will be monitored by the pressure transmitter and can be used to monitor seal performance and trigger an alarm.
  • Properties of the process fluid should be verified to avoid the possible blockage at the orifice plug.


  • 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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