Fluid is circulated by a pumping ring in the dual seal
Outboard seal acts as a safety backup to the primary seal .
Zero to very low process emissions .
No process contamination is allowed
Used with dual unpressurized seals .
High vapor pressure fluids ,light hydrocarbons
Heat transfer fluids
Piping loop must self-vent to vapor recovery /flaresystem
near atmospheric pressure .
Process vapor pressure generally greater than reservoir
Buffer fluid must be compatible with process leakage .
Primary seal leakage is indicated by increased vent pressure .
Reservoir level indicator shows outboard seal leakage .