BOOK_CONTENT
From Vacuum Technology: Calculations in Chemistry

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.

Table 3.1: Pressure ranges for vacuum pumps for chemical applications

Pressure range (mbar)

Pump type

10 +3 to 10 -3

Oil-sealed rotary pumps

  • Rotary vane/rotary piston pumps

    • 1-stage, p ult ~ 10 -1 mbar

    • 2-stage, p ult ~ 10 -3 mbar

Dry pumps

  • Piston pumps, p ult ~ 1 3 10 -2 mbar

  • Diaphragm pumps

    • 1-stage, p ult ~ 100 mbar

    • 2-stage, p ult ~ 8 mbar

  • Hook-and-claw and related pumps

    • p ult ~ 3 8 10 -1 mbar

Liquid ring pumps + gas ejectors [a]

  • p ult ~ few mbar

10 -3 to 10 -8

Diffusion pumps [b] , [c]

Turbomolecular pumps [b] , [c]

10 -8 to 10 -13

Cryopumps (cryopanels)

Turbomolecular pumps [c]

Diffusion pumps [c]

Copyright The Royal Society of Chemistry 2003 under license agreement with Books24x7

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Vacuum Pumps and Vacuum Generators
Vacuum pumps and vacuum generators provide sub-atmospheric pressure for a variety of industrial and scientific applications where a vacuum is required.
Mechanical Vacuum Pumps and Systems
Mechanical vacuum pumps and systems contain devices such as pistons, claws, scrolling spirals, and diaphragms to isolate and compress air.
Rotary Vane Vacuum Pumps and Systems
Rotary vane vacuum pumps and systems move media through the pump using a rotating assembly in the pumping chamber. Typically, there are two or more rotating vanes that move the media from inlet to outlet. Rotary vane vacuum pumps are positive displacement pumps.
Positive Displacement Pumps
Positive displacement pumps use a mechanical force such as gears, bladders, pistons, plungers or diaphragms to push liquid through and out of the pump.

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