F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
F04D—NON-POSITIVE-DISPLACEMENT PUMPS
F04D17/00—Radial-flow pumps, e.g. centrifugal pumps; Helico-centrifugal pumps
F04D17/08—Centrifugal pumps
F04D17/10—Centrifugal pumps for compressing or evacuating
F04D17/12—Multi-stage pumps
F04D17/122—Multi-stage pumps the individual rotor discs being, one for each stage, on a common shaft and axially spaced, e.g. conventional centrifugal multi- stage compressors