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API Plan 31

Recirculation from pump discharge through a cyclone separator, delivering clean fluid to the seal chamber and solids to pump suction.

API Plan 31


API Seal Plan 31 is like Plan 11 with a bypass from pump discharge via cyclone separator.

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Application Notes

  • Similar to Plan 11, with the addition of a cyclone separator.
  • Cyclone separator needs at least a 25 psi [1.7 bar] differential between pump discharge and the seal chamber for optimum performance.
  • For use with services containing solids with a specific gravity at least twice that of the process fluid.
  • The difference in pressure between the two separator outlets should be as close to zero as possible.
  • Maximum particle size in the process should be less than one quarter the size of the inlet orifice.
  • If the process stream is very dirty or is a slurry, Plan 31 is not recommended.
  • Solid particles are centrifuged from the stream and routed back to pump suction.
  • Cyclone separator must be monitored for abrasive wear which reduces performance.


  • Easy elimination of solid particles
  • Cyclone separator facilitates clean flush


  • Constant maintenance checks for cyclone separators required
  • Non-self-venting

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