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Screw compressors The principle for a rotating displacement compressor a screw was developed during the 1930s, when a rotating compressor with a high capacity and stable flow in varying conditions was required.

The screw element's main parts are the male and female rotors, which move towards each other while the volume between them and the housing decreases. Each screw element has a fixed, integrated pressure ratio that is dependent on its length, the pitch of the screw and the form of the discharge port. To attain the best efficiency the pressure ratio must be adapted to the required working pressure.

This is an example on how air is compressed in a screw compressor. In figure 1 air fills te space between the rotors, but for each turn the space does decreases more and more...

The screw compressor is not equipped with valves and has no mechanical forces that cause unbalance. This means it can work at a high shaft speed and combine a large flow rate with small exterior dimensions. An axial acting force, dependent on the pressure difference between the inlet and outlet, must be taken up by the bearings.

The screw, which originally was symmetrical, has now been developed in different asymetrical helical profiles.

This is an example of an oil lubricated screw compressor