Air Compressor classification, types and how to choose well


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The air compressor is one of the components integrated in a pneumatic network designed to supply compressed air to different tools so that they can work. To do this, it  sucks in the atmospheric air and treats it in a specific way inside . The objective? That at its exit, said air acts as a source of energy.

Subsequently, the air is cooled so that it occupies less volume before being stored in the boiler or tank. With this, the supply capacity of the pneumatic network is increased, increasing its efficiency. In the last entry of its Route 401 Blog , Loctite gives all the keys to this common device in workshops.

Compressed air compressor

The installation or use of an air compressor eliminates the need for an electrical supply. In addition, pneumatic tools are more durable tools, less sensitive to humidity and prepared for jobs in the automotive sector. Some examples of this are the application of paints, the sanding of surfaces or the blowing of the car bodies.

General ranking

According to the way they treat the sucked air, they are classified as follows:

  • Positive displacement compressor . This pet air compressor compresses it inside so that, upon its exit, the tendency of the air to return to its initial state of atmospheric pressure is used as a source of energy. This is the principle of operation of the most widely used air compressors.
  • Dynamic compressor . The air is sucked in so that, once inside the compressor, it is accelerated at high speed; the kinetic energy obtained is transformed into static outlet pressure that is used as an energy source.

In both types there are different types of compressors with a specific internal structure that is responsible for sucking in air, treating and compressing it, and releasing it.

Types of air compressors

The variety of compressed air compressors on the market is very high. The reason is that its operation and characteristics are very specific, with many different uses. The most common positive displacement compressors are:

  • The piston ones, with or without lubrication.
  • Screw type, with or without lubrication.

Other positive displacement compressors are  vane ,  variable speed  or  medium or high pressure compressors , among others. For their part, the most widely used dynamic compressors are divided into radial centrifugal technology   and  axial centrifugal ones .

Of all of them, Loctite analyzes the piston and screw ones for being the most used in the automotive sector.

1. Piston compressors

It is one of the most used in companies with moderate or medium compressed air consumption, such as mechanical workshops; also in some body shops and paint shops with few workers. Interestingly, many of the compressors marketed for domestic use feature this technology.

piston compressors

The internal constitution of these compressors is similar to that of heat engines in current vehicles. The aspirated air is directed, through an intake valve, into a cylinder in which there is a piston. This piston is attached to the connecting rod, which, in turn, is attached to a crankshaft; thus, the rotation of the crankshaft displaces the connecting rod and enables the piston to rise or fall within the cylinder.

The complete air compression cycle is divided into the following phases:

  1. Preparation for the aspiration of air  that is at atmospheric pressure. The piston rises to top dead center.
  2. Air suction . The intake valve opens and the piston begins to descend, generating air suction.
  3. Cylinder filling . The piston continues to descend until it reaches bottom dead center, at which point the cylinder is filled with air and the intake valve closes.
  4. Air compression and release of compressed air . With the valves closed, the piston begins to rise compressing the air; until the moment in which the exhaust valve is opened to expel the compressed air, which acts as a source of energy.

The main advantage of these compressors is their lower cost and the wide variety of models on the market. On the other hand, its efficiency is lower and it has a greater tendency to overheat with prolonged work. This can cause expansion or seizure in its internal components and requires rigorous maintenance.

2. Screw compressors

Also known as helical, they are equipment for industrial exclusive use. They are indicated for larger companies, being the most recommended option for sheet metal and paint shops. In addition, they are more efficient and quieter. Its main drawback is its cost.

The internal mechanism of this compressor is made up of an air inlet, two worm screws or helical rotors that mesh with each other and rotate inside a casing in the opposite direction, and an outlet for compressed air.

Air compression in this case is carried out in three phases:

  1. Air suction . The air from the outside enters through the suction side and is introduced into the chambers between the helical of the endless screws.
  2. Air compression . The air advances through the chambers and is compressed as the volume of said chambers is reduced.
  3. Release of compressed air . When the air reaches the last chambers, it is compressed and prepared to be expelled from the pressure side; It will be then when it can be used as a source of energy.

How to choose the air compressor?

It is important to assess, mainly, the type of work and use that is going to be given to it. In the first place, it is necessary to determine if the use that is going to give it is domestic (occasional) or industrial (frequent). Once this aspect is clear, the technical characteristics of the compressor must be assessed. The benefits may be lower in domestic uses, while in the industrial environment they must be increased and be consistent with the activity carried out.

Within the technical characteristics to be assessed, the following must be weighed:

  • The air flow  it is capable of supplying. It is generally measured in liters / min, but also in cubic feet / min or m3 / min.
  • The air pressure  it is capable of delivering, measured in bar or Psi (pounds per square inch).
  • The power  it possesses, represented in horsepower (power, steam, or kilowatts).
  • The storage capacity of  the boiler or tank, calculated in liters that it can store.
  • The type of starter  it presents, being able to be a direct starter or a star-delta type. The latter is the most recommended because it reduces the current peaks of the motors at the start of their operation and, therefore, the high electrical consumption in this phase. For this, this technology enables an initial start-up with a lower voltage (star), so that, once it has acquired certain revolutions, the offered voltage increases until it reaches its nominal operating value (triangle).


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