Calculation of the pumping speed of turbomolecular vacuum pumps by means of simple mechanical data

Abstract

A formula for simple calculation of a turbomolecular pump’s pumping speed is developed. The formula includes only mechanical data and a statistical factor k<1. The maximum limiting value of the pumping speed is obtained putting k=1. For this case pumping speed data are easy to calculate and to compare with those given by the manufacturer of a pump. With the aid of the kinetic theory of gases, values for k are computed for a usual case of blade shape and blade speed for different gases. The theoretical results for nitrogen are confirmed by measurements on single flow pumps. It is shown, that for light gases the arrangement of the disks with different shaped blades is of great importance. Results have shown that a high compression ratio does not guarantee a high pumping speed for hydrogen. Measurements on two new pumps confirm this relation.