The total time a pumping system needs to remove gas and reach a desired vacuum level. In the roughing phase, this time is dictated by chamber volume and the mechanical pump displacement. Once the system hits high vacuum, outgassing from the chamber walls becomes the dominant factor, making the time stretch out logarithmically.
Our pumping time to ten to the minus six has doubled since last week, so we either have a dirty chamber or a failing turbo.
Calculating theoretical pumping time for high vacuum is notoriously difficult because surface outgassing and virtual leaks usually add hours or days to the math.
Also heard as
- Pump-down time
Do not mix it up with
- Pumping speed: Pumping speed is the volume of gas removed per unit time, while pumping time is the total duration required to reach a target pressure.
Related terms
Pump down
To evacuate a chamber from atmosphere to its working pressure, through roughing, crossover and high vacuum.
Pump-down curve
Plot of chamber pressure against time during a pump-down, used as the fingerprint of a healthy system.
Pumping speed
Volume of gas a pump removes from its inlet per unit time, measured at the inlet pressure.
Outgassing
Slow release of gas from the surfaces and bulk of materials inside a vacuum system.