A method and a system control flow of fluid from a storage tank through a supply line to an end user. The system includes a valve that in its open position allows fluid flow from the storage tank to the end user and closes when the pressure in the fluid supply line drops below a predetermined set point. The storage tank is thereby isolated because the valve prevents fluid from flowing from the storage tank to the supply line when the pressure in the supply line is lower than a predetermined upper limit of the storage tank pressure. An end use that is particularly suited to the present system and method is a fuel storage and supply system for a natural gas powered internal combustion engine.