Why Double Mechanical Seals?

Double mechanical seals with a pressurized thermosyphon pot circulating a barrier fluid are used. The barrier fluid recalculates through the seal by heat convection generated as the pump shaft rotates through the seal. The barrier fluid in the pot is forced into the seal through the bottom line as the hot barrier fluid leaves the seal through the top line back into the pot. This arrangement will allow the seal to vent and ensure that the passages are full of fluid. The pot has a cooling coil which needs to be connected to chilled water allowing barrier fluid to cool before re-entering the seal. The pot is pressurized with the help of an inert gas like nitrogen.

Our pump seal design has a built-in pumping ring to enhance convection. This pumping arrangement is very necessary whenever oil is used as the barrier fluid because of oil's low specific heat and poor conductivity. Water is one of the best barrier fluid because of its high specific heat and good conductivity. There are several advantages of using double seal over the single seal arrangement.

The thermosyphon pot feeding the double seal is maintained at higher pressure than the stuffing box so if either seal fails, the barrier fluid would leak instead of the pumped fluid. Single seal failures allow pumped fluids to leak out in the atmosphere. Double seals can have five times the life of a single seal in severe environments. Also, the metal inner seal parts are never exposed to the process media so; toxic, hazardous and corrosive liquids are easily sealed without a need for expensive metallurgy.