Plan 52


Unpressurized buffer fluid system with double seal


  • Circulation is maintained by a pumping ring when equipment is energized, by thermosiphon effect when idle
  • No process contamination
  • No direct process fluid leakage to atmosphere

For use:

  • For media where process dilution is not allowed but leakage to atmosphere in diluted form may be allowed
  • Preferred for clean, non-polymerizing media with vapor pressure higher than buffer fluid pressure


  • Vessel vent must remain open to maintain buffer fluid pressure close to atmospheric pressure and vent the vapors to flare
  • Should not be used with dirty or polymerizing products
  • Restriction orifice in vent line maintains back pressure in pot to facilitate quick release of vapors to flare
  • Pressure switch setting should be above minimum flare back pressure to avoid false alarms
  • Never run the system when buffer fluid is low
  • Verify there is a temperature difference between the inlet and outlet lines to confirm flow
  • Vent system properly before start up