Study of water vapor pressure equilibration in a vacuum system

We have studied the approach to equilibrium pressure distribution after a sudden introduction of a given quantity of water vapor into a vacuum chamber. The time delay of a pressure reading of a spinning rotor gauge at the end of a 0.50 m and 0.935 m long stainless steel tube with inside diameter of 16 mm was measured. This time delay increased with decreasing pressure approximately as P−0.55. With a 0.5 m tube the time delay was approximately 5 times shorter than with a 0.935 m tube. At 1 × 10−4 mbar the times to reach a 99.7% level of equilibrium at the end of 0.50 m and 0.935 m tubes were 60 s and 330 s, respectively.

► A study of time delay to equilibrate water vapor pressure inside a vacuum chamber is presented.
► Use of SRG enabled high precision measurements of water vapor distribution in vacuum system.
► Resolution better than 0.3% was achieved in the range from 4 × 10−5 mbar to 2 × 10−3 mbar.
► Study is important for estimation of waiting time for comparison calibrations with water vapor.