A double mechanical seal is a combination of two seals mounted back-to-back, or one seal having both side sealing faces or tandem type. These seals can be single-coiled or multi-spring and can have a combination of unbalance/unbalance, unbalance/unbalance or unbalance/unbalance tandem types. These seals are ideal for the handling of 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 liquid being liquid pumped. The inner seal prevents the liquid from entering the system while the outer seal prevents it from leaking to the atmosphere.