The Agilent Variable Frequency Drive of the RP and RPS pumping system eliminates the need for separate pressure monitoring and switching-on of the root pump. By operating the roots pump at the correct rotational speed to optimize the gas flow to the backing pump as pressure is reduced, the 'knee' in the pumping speed curve of the backing pump / Roots pumping curve is eliminated, shortening pumpdown times, and reducing stress on the rotational elements.