A dry pump with two figure-eight rotors that turn in opposite directions without touching each other or the casing, carrying gas from inlet to outlet in the pockets between them. Its compression ratio is only a few tens, so it always sits on top of a backing pump and multiplies the system's speed in the 10 to 10⁻³ mbar range. Starting one from atmosphere needs a bypass line, a pressure switch or a frequency converter, or the motor overloads.
Don't start the Roots till the furnace is under 15 mbar or it'll trip on overload, this chamber's too big.
Also heard as
- Roots blower
- booster
- blower
- lobe pump
Related terms
Backing pump
Pump that keeps the exhaust of a turbo, diffusion or Roots pump below its maximum allowed pressure.
Compression ratio
Ratio of a pump's outlet pressure to its inlet pressure for a given gas, measured at zero net flow.
Roughing pump
Pump that takes a chamber from atmosphere down to the pressure where the high vacuum pump can take over.
Dry pump
Vacuum pump with no oil or liquid in its pumping chamber, used where oil vapour would contaminate the process.