Three‐stage Roots high vacuum pump

Abstract

A three‐stage Roots pump which has geometrical displacements of 305, 100, and 33 l/s is designed to extend the operating pressure region from 10 to 10−4 Pa. Mechanical features of the Roots pump are coaxial three‐stage design with minimum clearance seals for intermediate sealing between the first, second, and third stages without a lubricant; and computer designed flat‐waist‐cocoon shape rotors which enable more precise machining and narrower rotating clearances. To meet the requirement of hydrocarbon‐free pumping for many modern applications, especially sputtering, ion plating, and high intensity ion sources, a high throughput for different gases must be achieved occasionally at a higher pressure beyond the operating range of turbomolecular or diffusion pumps. The subject Roots pump has pumping speed of 220 and 260 l/s for nitrogen and helium, respectively, at 4100 rpm in the range of 1.3×10−3 to 4.0 Pa at the intake. The compression ratio is 104 for hydrogen, helium, and nitrogen, and an ultimate pressure is 1.3×10−4 Pa without bakeout.