Abstract: Screw-spindle vacuum pump with at least three closed-off feed chambers located one behind the other along each rotor and method for operating this compressor. The chamber which is last on the delivery side is brought virtually to the compression limit pressure by means of pre-admission, shortly before it opens towards the delivery side, by supplying a pre-admission stream which is at least five times as great as the intake mass stream. A precondition, in this case, is a minimum ratio of external compression to internal compression of five.

Abstract: The invention provides a two-rotors screw compressor having active cooling means on the pressure side of the motive rotor.

Abstract: A vacuum pump contains two rotary displacement rotor (8) that engage each other, in particular in a convoluted manner, inside in expansion chamber through which flows a stream in the axial direction. The rotors are mounted in cantilever at the delivery side and are linked each to a driving motor (35, 36). Each rotor (8) forms together with its shaft (20), a stationary bearing body (7) and a bearing (21, 22) delimited by the shaft (20) and the bearing body (7) a module that may be removed as a single unit from the housing (3). The rotor (35) of the driving motor is preferably also part of said module.