SRD FAQ #13

This is the Low Pressure Purge (LPP). It is there for a number or reasons:

• A blanket of N2 is maintained in the drain box for proper resistivity readings during the rinse cycle.
  
  
• N2 is kept flowing past the N2 heater until it is cool. (Result:heater lasts longer and stays cleaner).
  
  
• Maintaining positive N2 pressure in the bowl.