The limiting pressure a pump approaches with its inlet blanked off or connected to a small, clean test dome after a long pumping time. Data sheets state it as total or partial pressure, with or without gas ballast, for example about 2×10⁻³ mbar for a two-stage rotary vane pump. A real chamber never reaches its pump's ultimate pressure because outgassing, leaks and conductance losses all add to the load.
Datasheet ultimate is 1E-10, but on our chamber with that long elbow we'll be happy with 1E-8.
Also heard as
- ultimate
- ultimate vacuum
Related terms
Base pressure
The lowest pressure a particular chamber reaches after pumping for a set time with no process gas flowing.
Compression ratio
Ratio of a pump's outlet pressure to its inlet pressure for a given gas, measured at zero net flow.
Blank
Solid flange with no hole, used to seal an unused port or to test a pump on its own.