Vacuum Science and Technology (VST), e-chapter 4 Vacuum pumps and pumping systems
The chapter extensively discusses all nowadays commercially available pump principles at the hand of important qualities, such as throughput, pumping speed, ultimate pressure, compression ratio, gas type dependency and working range. In addition, more specific characteristics of a particular type of pump are discussed in the section treating this pump.
Since the 1980’s the pump palette has made a clear shift from wet to dry pumps. With ‘wet’ we mean pumps which need a liquid for their pumping action. Liquids in pumps because of several reasons (unsurmountable contamination problems, increasing costs of maintenance and ever higher environmental costs because of stricter regulations) became impermissible in various applications of vacuum in research and industry and gave a great impetus to the development of dry pumps. Transition from wet to dry pumps nowadays is considered as an economically attractive alternative.
With respect to the Dutch version of this book from 2000, the chapter contains several major changes and significant innovations. In summary, the chapter is extended with attention to the multi-stage Roots pump, which in the past decade has rapidly developed into a valuable alternative to the claw pump and is able to discharge to atmospheric pressure. As for the claw pump, new insights are incorporated about the use of an integrated combination of Roots and claw stages. Concerning the screw pump, attention is paid to the tapered pitch as a solution to reduce the heat generated by isochoric compression. The section ‘Molecular pumps’ is extended with a paragraph on the molecular drag pump (MDP)/side channel pump combination, consisting of a Holweck type molecular drag pump and multiple stage miniature type of side channel blower. This pump combination also appears to be able to discharge against atmospheric pressure. The required knowledge regarding the side channel blower is added to the section ‘Dry rotary pumps’. Finally, the section ‘Sputter-ion pumps’ is supplemented with information on the so-called ‘Galaxy’ and ‘StarCell’ cathode structures to increase the pumping speed for noble gases.