To get a better vacuum you need either a booster pump, sealing liquid with a lower vapor pressure, or an added heat exchanger. These pumps require timing gears. Use these designs to about 200 mm Hg. Often used as a booster pump. No contact between the rotating lobes reduces wear problems.
Corrosive gases combined with condensation can cause severe corrosion problems.
Powders in the gas stream present fewer problems than other vacuum pumps because of the non-contacting parts. These pumps are environmentally friendly because they exhaust only what they take in. They do not add water, oil or other liquids to the gas stream Can be used in both gas and pressure applications. Low cost to operate and reasonably energy efficient. Limited by depth of vacuum and corrosion problems.