API Plan 31

In this type mechanical seal flush plan is used for the pumping fluid consisting of solid particles. The flushing fluid from pump discharge is passing through a cyclone separator for separating the suspended solids from the pumping fluid. Centrifuged solid particles are returned to pump suction from the cyclone separator. Seal chamber heat is flushed by the fluid from the cyclone separator. This type of flushing plan is used for dirty or contaminated fluids, water with sand or pipe slug etc..,

Cyclone separator works best on solids with a specific gravity twice the process fluid. Seal chamber pressure must be nearly equal to suction pressure for proper flows. The piping should not include an orifice and is not expected to vent the seal chamber.

API Flushing Plan 31


  • The solid particles density must at least twice the pumping fluid density.
  • Very close throttle bush clearance to be maintained.


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