Patent ID: 8393854

Claim:
A vacuum pump comprising a first pumping section, a second pumping section downstream from the first pumping section, a third pumping section downstream from the second pumping section, a first pump inlet through which fluid can enter the pump and pass through each of the pumping sections towards a pump outlet, and a second pump inlet through which fluid can enter the pump and pass through only the second and the third pumping sections towards the pump outlet, wherein the third pumping section comprises a helical groove formed in a stator thereof, the second pumping section comprises a helical groove formed in a rotor thereof, and the first and second pumping sections are sized substantially the same in a radial direction, such that the second pumping section that has the helical groove formed in the rotor thereof is able to increase a pumping capacity without a corresponding increase in size, wherein a depth of the helical groove on the rotor at an inlet side thereof is greater than a depth of the helical groove on the stator at an inlet side thereof.