A double mechanical seal is a combination of two seals mounted back to back or a single retainer having both sides sealing faces or tandem type. These seals can be single-coiled or multi spring and can have a combination of unbalanced/unbalanced, unbalanced/balanced and balanced/balanced type seals. These seals are ideal for handling toxic /abrasive media. To cool the sealing faces during operation a clean compatible liquid is circulated between the two seals at a pressure higher (by one bar ) than the process fluid. The inner seal prevents the barrier fluid from entering the system while the outer seal prevents it from leaking into the atmosphere.The circulation of barrier fluid is done with the help of Thermosyphon or Forced circulation pump.