ABSTRACT
Vacuum system for producing of low and medium vacuum (Fig. 6.4) have two vacuum pumps. Pump 7 produces medium vacuum and pump 1 provides preliminary rarefaction. As a medium vacuum pump, one may apply two-rotor, vapor-jet, or adsorption pumps (Table 6.2). Pumps 1 should provide low vacuum. The speed and the limiting pressure of the preliminary rarefaction pump should be in accordance with the characteristics of the medium vacuum pump. The optimum efficiencies of two-rotor pumps depending on the effective pumping speed and the number of sequentially connected elements are shown in Fig. 6.5.
