the invention relates to a rotary screw machine that is completely oil - free . known rotary screw machines with cooling , sealing , lubrication of the screw rotors and oil - lubrication and oil - cooling of the bearings have been replaced with water - lubricated and water - cooled bearings . each screw rotor is mounted in a water - lubricated radial slide bearing and one trunnion of the rotor co - acts with a water - lubricated thrust bearing which acts both as an hydrodynamic and an hydrostatic bearing . the trunnion bearing housing is in fluid connection with the rotor housing , both along the trunnion and via a conduit from the bearing housing interior to the gas inlet of the screw rotor or via a channel which is cut - off from said inlet .