Aerzen Screw Compressors are available as oilfree machines in various sizes, single- and multi-stage for the most different cases of application. Oil-injected Screw Compressors also belong to our Sales program.

The Aerzener Maschinenfabrik has been manufacturing screw compressors functioning on the Lysholm principle since the year 1943. Initially, the only types produced were machines that were designed to convey the medium with complete freedom from any contamination by the lubricating oil. In the year 1968, after many years of intensive development work, the screw compressors manufacturing program was enlarged to include compressors of a similar type, but operating on the principle of oil injection. These are our series VMX and VMY machines.

Aerzen Screw Compressors are excellently suitable for dry and clean compression of air and neutral gases. As high-developed serial products Aerzen Screw Compressors are used in all the branches of the industry and cases of application, as e.g.:

• pneumatic transport
• aeration of sewage basins
• vacuum generation in glass industry
• keeping seas and harbours free from ice
• construction of oil traps
• gas-air mixing plants
• production of medicine
• stationary unloading of silo vehicles
• beverages industry
• chemistry
• petrochemistry
• and many more

How the Aerzen Screw Compressor operates

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=viχ

Compression process

• Suction intake
  Gas enters through the intake aperture and flows into the helical grooves of the rotors which are open.
• Compression process
  As the rotation of the rotors proceeds the air intake aperture closes, the volume diminishes and pressure rises.
• Discharge
  The compression process is completed, the final pressure attained, the discharge commences.

Rotor-profiles of Aerzen Screw Compressors

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.

Volume control for Aerzen Screw Compressors

In principle, it is necessary to consider the problems of volume control for dry-running and for oil injection type screw compressors separately.

Volume control for dry screw compressors

Control by variable speed:
In consequence of the fact that screw compressors displace the medium positively, the most advantageous method of achieving volume control is that obtained by variable speed. This may be done in any of the following ways:

• by variable speed electric motors
• by use of a torque converter
• by steam turbine drive

Speed may be reduced to about 50 % of the maximum permissible speed. Intake volume flow and power consumption are in this manner reduced in approximately the same proportion.
Control by bypass: Using this method, the surplus gas volume is allowed to flow back to the intake side by way of a governor that is controlled by the admissible final pressure. An intermediate cooler cools back the surplus gas volume down to the intake temperature.

Full load/idling speed governor:
As soon as a predetermined final pressure is attained a pressostat operates a diaphragm valve which opens up a bypass between discharge- and suction side of the compressor.
When this occurs, the compressor idles until pressure in the system drops to a predetermined minimum value, whereupon the valve will close once again on receiving an impulse from the pressostat, thereby bringing the compressor back onto full load once again.

Suction throttle control:
This method of control is suitable for air compressors only. As in the case of the full load/idling speed control method, a predetermined maximum pressure in the system, for example in a compressed air receiver, causes pressure on the discharge side to be relieved down to atmospheric pressure. Simultaneously, the suction side of the system is throttled down to about 0.15 bar absolute pressure. When pressure in the whole of the system has dropped to an admissible minimum value, full load is restored once again.

Control of screw compressors equipped with oil injection

Suction throttle control:
Since final compression temperature is governed by the injected oil, a greater range of compression ratios such as may arise when the induced volume is throttled down, can be safely coped with. This permits the main flow volume to be varied infinitely within wide limits. This particular type of control is the one to be preferred for compressors of the VMX series.