Even though there are many different models of air compressors, there are only three different types. Each type has its advantages and drawbacks. Picking the right air compressor when setting up a compressed air system is crucial. Not only can you face the risk of getting a substandard system with to low air flow, excessive noise and high power consumption, but you also run the risk of buying a compressor that will wear out early and be to expensive to both operate and purchase.
This article will cast light on which air compressor types that will be suitable for different compressed air systems.
We can, as said earlier, divide air compressors into three different types:
- Reciprocating air compressors
- Rotary air compressors
- Rotodynamic air compressors
Each of the three compressors have very different characteristics making them ideal within their own field.
Reciprocating compressors:
These compressors are commonly known as piston- or membrane compressors. They are called that because they have either a piston, or a membrane, that is being pushed up and down inside a compression chamber to compress air. They are known to be very robust and can operate for many years with minimum maintenance. Their low price and work pressure (normally 8 bar) makes them ideal for carpenters, DIY home improvement, small garages and workshops. You can even find bigger models in industry and production plants.
In the picture to the right: Campbell Hausfeld Piston Air Compressor
Rotary air compressors:
Rotary air compressor consist of for different compressor principles: scroll, vane, lobe and screw compressors. The most common air compresor for industry is the screw- and scroll compressor, while vane and lobe compressors are more common in laboratories and medical industry. The screw compressor compresses air by rotating a screw, which is interlaced with another screw, inside a compression chamber. This rotating motion creates air pockets in-between the two screws and the compression chamber. As the screw is turned by the compressor motor, the air pockets volume gradually decreases, compressing the air trapped in the air pocket. At the end of the compression chamber the trapped compressed air is released into the compressed air system. Unlike most other compressors, screw compressors use air compressor oil to cool the compressor, and to lubricate and seal gaps between the screw and compression chamber.
The scroll compressor works by having to mirrored interlaced spirals, mounted on each its plate, rotating in opposite direction with one spiral slightly off center. Air is trapped between the interlaced spirals and because of the direction of the spirals rotation, the trapped air is guided in towards the center of the two spirals. As the air is lead inwards the air pockets volume gradually decreases, resulting in an increase in the air pressure. At the center of the two spirals the air is "vented" into the compressed air system. The screw compressor is ideal for industry and for compressed air systems with high consumption, such as in a spray booth or when using air tools like jackhammers. The scroll compressor has a lower air flow and can be more or less compered to the piston compressor. Its advantage to the piston compressor is that it runs much quieter.
The scroll compressor works by having to mirrored interlaced spirals, mounted on each its plate, rotating in opposite direction with one spiral slightly off center. Air is trapped between the interlaced spirals and because of the direction of the spirals rotation, the trapped air is guided in towards the center of the two spirals. As the air is lead inwards the air pockets volume gradually decreases, resulting in an increase in the air pressure. At the center of the two spirals the air is "vented" into the compressed air system. The screw compressor is ideal for industry and for compressed air systems with high consumption, such as in a spray booth or when using air tools like jackhammers. The scroll compressor has a lower air flow and can be more or less compered to the piston compressor. Its advantage to the piston compressor is that it runs much quieter.
Rotodynamic air compressors:
These compressor are quite common because of their small size and incredible air flow. These compressors are the ones you would find mounted on a combustion engine and in the working end of a turbine. This compressor type is basically an air pump, but unlike a pump it's capable of creating air pressure high enough for fuel to self ignite. We divide this compressor type into two: 1. centrifugal compressor and 2. axial compressor. The centrifugal compressor is what you would typically find on a car engine. The centrifugal air compressor sucks in air at the center of it housing, accelerating it inside the compressor house with its impeller (fan wheel) before the air is jettisoned out of the side of the compressor, through a diffusor disc. The rapid speed decrease that happens over the diffusor disc is what causes the pressure increase. An axial compressor works much after the same principle, but instead of the air being ejected out on the side of the compressors, it's being sent strait back and ejected in the other end, where a diffusor disc slows down the air speed and causes an increase in the air pressure. The centrifugal compressor is common in tight spaces that requires extremely high air flow. For this reason it is often the choice in combustion engines on cars etc. The axial compressor is is used in turbines and heavy industry like petroleum refineries and production plants.
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