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Vacuum System Evacuation to Base Pressure
Author(s) -
Grinham Rebecca,
Chew Andrew
Publication year - 2018
Publication title -
vakuum in forschung und praxis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.213
H-Index - 13
eISSN - 1522-2454
pISSN - 0947-076X
DOI - 10.1002/vipr.201800666
Subject(s) - drag , header , atmospheric pressure , base (topology) , vacuum pump , chemistry , chamber pressure , analytical chemistry (journal) , volume (thermodynamics) , vacuum chamber , pressure measurement , ultra high vacuum , mechanics , materials science , thermodynamics , composite material , meteorology , nanotechnology , physics , chromatography , mathematical analysis , statistics , mathematics
Summary A study has been made to compare the times taken to evacuate a turbomolecular and scroll pumped chamber to a base, high vacuum, pressure. A small test header (26.7 litre) was evacuated via two different paths: through a fore‐line, switching paths once ‘cross‐over’ pressure was reached, and directly through a turbomolecular pump (TMP) where the TMP was not operational until cross‐over pressure was reached. When starting the TMP/switching paths at 0.1 mbar, pump‐down times were significantly slower through the TMP; the time taken to reach 0.1 mbar increased by between 2 and 8 minutes dependent upon the TMP model (from a 24% increase in time with nEXT300 to a 232% increase for the nEXT240). For pressures below 8 · 10 −6 mbar there was no significant difference in required pumpdown time between the two methods. The variation between methods being less than the ±30% uncertainty in pressure gauge measurement. The increase in pumpdown times to achieve pressures down to 10” 5 mbar when evacuating through the TMP was seen for all TMP models tested, however a greater difference was seen for a TMP configured with Holweck drag stages than those containing Siegbahn drag stages. The best pumpdown time for pressures down to 10 −5 mbar was achieved when pumping through the TMP whilst allowing the TMP to ‘start’ operation from atmospheric pressure.