Turbomolecular pumps calculations

A turbomolecular pump with a DN 63 ISO-K inlet has a pumping speed for N2 of 115 L s 1. It is to be connected directly to a system used for obtaining outgassing data. For this application, the effective pumping speed of the pump is to be reduced to 50 L s"1 by inserting a plate with a circular aperture in the flange. Calculate the diameter of the aperture. 

A turbomolecular pump (S0 = 200 Ls"1 for N2) is fitted to a mass spectrometer via 200 mm of pipe with a diameter of 102 mm (DN100). Calculate the pumping speed of the TMP at the mass spectrometer. 

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. 

The ultimate total pressure that can be attained by means of turbomolecular pumps mainly depends upon the partial pressures of the various gases on the pre-vacuum side of the turbo-molecular pump. The partial pressure p0 of a gas on the high-vacuum side is calculated from the partial pressure ppatt on the fore-vacuum side, divided by the compression for this gas acording to (41). 

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