The screw compressor has two rotors, a main rotor (1) with fins a secondary rotor (2) with grooves. They are fitted in a casing with two intersecting parallel cylindrical borings to receive them in a cavity sealed by end walls. There is a relief groove (4) on the compression side (D) in each foot base (3) of the grooved rotor. This groove may extend out from the centre line in the direction of the profile flank running ahead of it. The relief groove may have an endface radius of 3-6 mm.
