A screw compressor is a twin-shaft rotary piston machine functioning on the principle of positive displacement combined with internal compression.

The medium handled is conveyed from the suction port to the discharge port entrapped in ever diminishing spaces between the convolutions of the two helical rotors, being thus compressed up to the final pressure before it is discharged into the discharge nozzle.

The spaces referred to are those formed between the cylinder walls and the interlocking convolutions of the two helical rotors. The position of the edge of the outlet port determines the so-called “built-in volumetric ratio” vi. The built-in compression ratio πi results from the equation πi=vi to the power of kappa.

The rotors having asymmetrical profile are manufactured on special tool machines with highest accuracy. So, optimum volumetric efficiencies are guaranteed. The rotors are dynamically balanced.

Aerzen determines the rotor profiles according to the main field of application, where for example for large flow volumes and small differential pressures the most favourable profile combination 3 + 4 is selected. The male rotor has 3 teeth, the female rotor 4.

For larger differential pressures as well as for process gas compressors profile combination 4 + 6 is always applied.