simultaneously from multiple containers become depleted at approximately the same time according to embodiments of the present invention many suitable controls may be used to achieve the desired effects responses and overall system performance according to one embodiment the difference in net weights of the containers is monitored by an automatic control system such as a programmable logic controller plc if the difference exceeds a predetermined value the container with the least weight is temporarily shut down and gas is withdrawn only from the heavier container s once the difference in container weights is within specified limits the container that was shut down is restarted if the system senses that the required flow rate is greater than that which may be sustained from the remaining on stream container s when the lighter container has been taken off stream then this feature may be temporarily disabled so that flow from the system is not interrupted for instance if the supply pressure falls below a predetermined value then this feature may be temporarily disabled in another embodiment another control strategy for balancing the flows is similar to the control strategy described above in that the difference in net weights of the containers is monitored by an automatic control system such as a plc for this strategy the control system responds by adjusting the temperature set points of the container heaters based on the difference of the net weights of the containers in a preferred control strategy a cascade type control is used in which a container pressure is substantially maintained by a pressure controller which adjusts the heater temperature set point for that container the pressure set point for one container may be held constant while the pressure set point for the other.