External purge system for a tank train

Abstract From the Canadian patent

A novel purge system for a string of tank cars wherein purge gas is directly introduced into the vapor space of each tank above the cargo in the tank and wherein the purge gas is not bubbled through the cargo but is supplied directly to the vapor space above the cargo and forces the cargo out the vent pipe at the end of the car to the next car to successively assure that the proper level of cargo and the proper pressure of the purge gas is maintained in all of the cars. Since the gas is not bubbled through the cargo, gas will not be stored in the cargo and the pressure requirements will be substantially reduced as compared to bubbling through the commodity and the volume of gas required …