The main features are:

able to pump gases and vapours;

nearly isothermal compression of gases;

no lubricant in contact with pumped gas;

the pumps must be continuously fed with service liquid, normally water (oil, organic liquids etc. can be used), while working in a sufficient rate to eliminate the heat produced by the compression of gases and to replace any liquid which flows out of the pump together with the gas. The service liquid can be separated from the gas in a liquid separator and can be recirculated either partially or entirely, after intermediate cooling;

safe operation and minimum maintenance;

reduced noise and vibration.