Study of a scroll vacuum pump (difference in the ultimate pressure with the species of gases)

In order to examine the pumping performance of the scroll pump for various gases, the following two experiments were performed: (1) Measurement of the ultimate pressure for Argon, Nitrogen and Helium; (2) Separation of the direct effect of orbiting speed on the ultimate pressure from the effect of clearance change with temperature change accompanying a variation in orbiting speed. For these experiments, the apparatus was improved as follows: (1) The pump was strengthened with double seals to prevent leakage from the atmosphere; (2) A dry ice trap was put between the vacuum chamber and the vacuum gauge for the purpose of removing the water vapor; (3) A tank connected to the discharge mouth is filled with test gas, whose pressure is a little higher than the atmosphere, in order to avoid other-gas contamination. The results were compared with the theoretical predictions, and the validity of the theory was confirmed to a certain extent.