Screw compressors

A screw compressor is a type of rotary compressor which compresses the air through the screw pair. The main advantage of it is that it can continuously supply compressed air with minimum pressure fluctuations.

Construction:

The screw compressor consists of:

  • two screw elements that rotate
  • body
  • air filter
  • rubber sealers
  • inlet and outlet valves

Principle of work:

In a screw compressor one of the shafts is driving and the other driven. A driving shaft is connected to the driven shaft by means of gears, thereby it controls the speed of both shafts. Usually the driving shaft is powered by an electric motor. The screw pair is in sealed housing.

At first the inlet valve is open for air supply. Then a motor that activates the driving shaft turns on. Driving shaft in turn causes the driven shaft to rotate. The air enters the gap between the two screws. When the screws rotate, the gap between them decreases, which leads to the air compression. Also, thanks to screw action air moves from the inlet valve to the outlet. When compressed air reaches the outlet valve, it enters a storage tank.

In addition, during the air compression process a compressor casing is heated. Cold oil constantly flows around it and cools a compressor body. The reason of heating the compressor is that the efficiency of any compression process will be larger if it is performed isothermally in difference from an adiabatic or polytropic process. Thus, for keeping an air temperature during the air compression, excessive heat is constantly drained by oil or air.

Benefits and drawbacks of screw compressors:

If we compare piston compressors and screw compressors, that screw compressors have the following advantages:

  • they operate noiselessly and do not form strong vibrations;
  • small size and light weight;
  • if there is an automatic control system, they do not require a permanent staff support;
  • energy-efficient;
  • cooled by air or liquid.

The main disadvantage of screw compressors is the high price of its details, manufacture and repair

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