3.1 INTRODUCTION

Vacuum pumps, either singly or, more usually, as part of a pumping system, create and maintain the conditions appropriate to a required process. Each of the types of vacuum pump available has a characteristic working range in which it is effective. Outside that range, shortcomings in performance become apparent.

In this chapter, those pumps that are frequently encountered throughout the range of vacuum pressures are dealt with (see Table 3.1). Where necessary, to support the calculations, the operating principles and pump characteristics are reviewed. With gas-transfer pumps operating in the HV/UHV range (typically diffusion or turbomolecular pumps), continuous operation of backing (forevacuum) pumps is required for efficient performance. In such cases, the combination is considered.