To avoid using elaborate tandem or double-acting arrangements with their related auxiliary units for hazardous media, operators are allowed in certain cases of application to operate with a so-called "gas seal" as a safety seal. This dispense with the buffer medium quench with attendant buffer system that would otherwise be needed. In practice the gas safety seal is installed in tandem arrangement downstream from a main seal, whose leakage is removed via a leakage line (leading, in the case of liquefied gases, to the flare). Incorporated in the leakage line is a pressure switch, which triggers an alarm signal should the pressure rise due to increased leakage or failure of the main seal and normally shuts down the working pump either at once or after switching over to the standby pump. It should be noted that gas safety seals of this type cannot be monitored continuously during normal operation due to the absence of buffer medium. At the moment of demand it is not possible, therefore, to count on 100-% standby of the gas safety seal (e.g. for safety analyses of systems etc.). This is where conventional tandem or double-acting arrangements have their major advantage.

Gas safety mechanical seal