To fully maximize the benefits of an air compressor, you should know the basic types of air compressors and how it works, thus, giving you the power to choose.
SAE categorizes air compressors into two main divisions: Positive Displacement Air Compressors and Dynamic Air Compressors.
Positive Displacement Air Compressors increase the pressure of the air by reducing its volume. This means they are taking in successive volumes of air which is confined within a closed space and elevating this air to a higher pressure.
SAE offers three types of Positive Displacement Air Compressors:
The piston compressor is one of the earliest compressor designs, but it remains the most versatile and is still a very efficient compressor. The piston compressor moves a piston forward in a cylinder via a connecting rod and crankshaft. If only one side of the piston is used for compression, it is described as single acting. If both sides of the piston, top and underside are employed, it is double acting.
The versatility of the piston compressors knows virtually no limits. It compresses both air and gases with very little alterations. The piston compressor is the only design capable of compressing air and gas to high pressures, such as breathing air applications.
The configuration of a piston compressor can be a single cylinder for low pressure/low volume to a multi-stage configuration cable of compressing to very high pressure. In these compressors, air is compressed in stages, increasing the pressure before entering into the next stage to compress the air into even higher pressure.
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The screw compressor is a displacement compressor with pistons in a screw format; this is the predominant compressor type in use today. The screw compression element main parts comprise male and female rotors that move towards each other while the volume between them and the housing decreases. The pressure ratio of a screw is dependent on the length and profile of the screw and of the form of the discharge port.
The screw element is not equipped with any valves and there are no mechanical forces to create any imbalance. It can therefore work at high shaft speed and combine a large flow rate with small exterior dimensions.
Based on traditional, tried and tested technology, the vane compressor is directly driven at very low speed (1450rpm), offering unrivalled reliability. The rotor, the only continually moving part, has a number of slots machined along its length into which fit sliding vanes that ride on a film of oil.
The rotor rotates within a cylindrical stator. During rotation, centrifugal force extends the vanes from their slots, forming individual compression cells. Rotation decreases the cell volume, increasing the air pressure.
The heat generated by compression is controlled by pressurised oil injection.
The high pressure air is discharged through the outlet port with the remaining traces of oil removed by the final oil separator.
Centrifugal Compressors are not positive displacement compressors like the Reciprocating, Screw or Vane Compressors. They use very high speed spinning impellers (up to 60,000 rpm) to accelerate the air then diffuser to decelerate the air. This process, called dynamic compression, uses velocity to cause an increase in pressure. In most Centrifugal compressors, there are several of these impeller/diffuser combinations. Typically, these machines have intercoolers between each stage to cool the air as well as remove 100% of the condensate to avoid impeller damage due to erosion.
Animation and text taken from Cameron Corporation.
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