Abstract: The invention deals with a screw compressor with housing, such housing containing a working chamber with two parallel cylindrical intersecting bore holes. The working chamber is bordered by two even end walls vertical with the longitudinal axes of the bore holes; two helical or screw rotors are arranged in the working chamber revolving and engaging and sealed against the chamber walls so that they do not touch the latter, whereby there is axial clearance due to the manner of construction between the frontal walls of the chamber and the fronts of the helical part of the rotor, whereby the screw compressor is provided with a control for volume which causes the output to be decreased by returning the gas sucked into gaps to the suction chamber before compression starts.