Abstract: In a two-stage vacuum pumping system having a single drive motor powering both stages, a by-pass line connected between the container being evacuated and the interstage line between the two stages for relieving excess pressure in the interstage line during the initial pressure pull-down of the container. This reduces the load on the second stage pump and thereby lowers the power requirements of the drive motor. A pressure switch actuated solenoid valve in the by-pass line, which is in the open position during the pull-down procedure, is closed when the container is evacuated to a set-point pressure. When the by-pass line is closed off the two stages work together to pump down the container to a desired pressure below the pressure switch set point.