What are some differences between different compressors

Compressor: function, types

Compressors belong to the fluid energy machines and are required to compress different gases mechanically. This means that they increase the pressure of the gas and at the same time decrease the volume. Because of their function, they are also called air compressors. Therefore they are related to pumps that increase the pressure of liquids.

Synonym (s): compressors, air compressors, compressors

Difference between compressor and compressor

Colloquially and on many websites, compressors are equated with compressors. Strictly speaking, however, the compressor is just a technical part of a compressor. It can therefore be said that there is always a compressor in the compressor. Nevertheless, in the following and on the compressor sub-pages, the terms compressor, air compressor and compressor are equated for the sake of simplicity.

functionality

According to the Duden, compressors are devices for compressing gases and vapors. This means that the gas volume is reduced by squeezing. The compressor alternates between sucking in and compressing the gas. The sucked in gas volume V1 can be compressed to a reduced volume V2 by the operating pressure p1 of the compressor. The increased pressure p2 and the density of the gas lead to a heating of the gas. The compressor compresses the air into powerful compressed air, which is normally measured in liters.

construction

The motor that drives the compressor is decisive for the structure and function. The advantage of a compressor is that it does not directly expel the compressed gas. Thanks to an attached pressure vessel into which the compressed air is pumped, larger quantities of gases can be stored. This means that the compressor motor does not have to be in continuous operation. The pressure in the compressor tank is checked by means of a manometer. If the pressure falls below the previously set minimum, the motor starts again automatically and fills the boiler with new, compressed gas. The other way around, the motor stops when the value of the maximum pressure is reached. There is also a solution for overpressure: In this case, a safety valve opens, allowing gas to escape.

Things to know before you buy

Compressors differ in their pressure and the achievable delivery volume, which results from the air volume released per unit of time (m3 / min or liters / min). In general, the following applies: the larger the compressed air tank, the higher the performance of the compressor. In addition to the delivery quantity and the operating pressure, the pressure ratio and the degree of delivery are also important depending on the use. As already mentioned, the delivery pressure describes the volume of the expelled gas per unit of time, while the operating pressure is the overpressure that can be achieved within the compressor. The pressure ratio results from the ratio between final pressure and suction pressure and the difference between the actually conveyed and theoretically achievable volume flow can be determined from the degree of delivery.

In summary, the following factors must be considered before choosing the right compressor depending on the task and air content:

  1. filter: In order to avoid bubbles on the painted surface of the compressor, filters and refrigeration dryers to filter impurities and dirt from the compressed air are essential.
  2. Boiler size: If the vessel is too small, the air pressure is too weak, with which some work cannot be carried out in the first place. In addition, the compressor is under permanent high pressure and often switches itself off to protect itself from overload. The permanent switching on and off leads to a high level of wear.
  3. quantity delivered: The delivery quantity defines the performance.
  4. Filling volume / air volume: In order to achieve more than 100 liters of compressed air per minute, the vessel must not be too small. Impact screws and chiselling work, for example, require a filling quantity of at least 150 l / min. The filling capacity is therefore the amount of compressed air that a compressor makes available as compressed energy.
  5. Suction power: The basic rule here is: It must be possible to pump in 30 percent more air than the maximum that can be expelled again.
  6. Pressure range: There are compressors with a working pressure between 6 bar and over 10 bar. The area of ​​application determines how much of it is needed. A high pressure range is common in the commercial sector. A compressor that is to be used to inflate a truck tire must be able to generate a working pressure of 16 bar.

Questions about the right compressor selection

  • Duration and frequency of operation?
  • Does the filling capacity match the type of use?
Required boiler size?

The required boiler volume of the air compressor depends on the application. There are compressors with tanks of different sizes that hold between 20 l and 300 l of boiler. If the compressor is in continuous operation, a compressor with a large volume of boiler is required. A 20-liter container is sufficient for work such as painting. A vessel is not necessary for some work.

Need a particularly low-noise or mobile model?

If you need a particularly low-noise model, you should use the so-called whisper compressors. On average, they reach a volume of 50 dB and are therefore 90 to 98 percent quieter than conventional air compressors.

Whisper compressors are available both with and without oil.

application areas

DIY with compressors: My workshop 2.0 and the long-term experience with my compressor

Here are some areas of work where compressors are beneficial:

  • Interior construction & construction site (building trade and renovation): Craftsmen, DIY enthusiasts and employees from production choose compressors as compressed air tools. They make screwing, stapling, nailing nails and grinding easier (e.g. with a pneumatic nailer, pneumatic stapler and chisel hammers for wall openings)
  • Car workshop: Impact wrench for loosening wheel nuts when changing tires, compressed air devices (air compressors) for measuring tire pressure and inflating car or bicycle tires. Tire inflation meter.
  • Painting and varnishing work: Avoidance of color bleeding with compressed air spray guns
  • Cleaning: high pressure pre-wash by air compressors for cleaning vehicles or masonry
  • Doctors' offices and laboratories: dental compressors
  • Metal crafts and metal industry
  • Refrigeration: refrigerators and air conditioners


Depending on the application, the pressure vessel must be correspondingly large. A large pressure vessel is selected for continuous operation. For sporadic use, for example for inflating tires, a compressed air compressor without a compressed air tank is sufficient. For painting work, however, the compressed air tank must have a capacity of at least 20 liters.

species

Oil-driven and oil-free compressed air compressors

In addition, compressors are differentiated on the basis of oil-driven and oil-free displacers. Oil-lubricated air compressors are advantageous in permanent operation, such as in the trade. The air mixed with oil is not a problem for rotating and hitting activities. For painting work, however, only oil-free compressors can be used.

Hermetic and open compressors

Another difference arises in the refrigeration technology. Fully hermetic and semi-hermetic as well as open compressors are used there. With the fully hermetic compressor, the motor and compressor of the compressor are located together with the refrigerant in a closed housing. In the case of semi-hermetic compressors, on the other hand, the motor is located outside the housing. Open compressors are in turn driven by belts, gear wheels or a gearbox.

Depending on the design, different types of compressors are distinguished, e.g. B .:

  • Positive displacement compressors
    • oscillating
      • with crank operation
        • Rotary piston compressor
        • Reciprocating compressors
      • without crank operation
    • rotating
      • single-wave
        • Scroll compressor
        • Multi-cell compressor
        • Liquid ring compressor
        • Free piston compressor
      • multi-wave
  • Turbo compressors
    • Axial compressor
    • Radial compressor

Other designs

  • Liquid ring pump
  • Reciprocating compressor
  • ionic compressor
  • Lamellar compressor
  • Rotary compressor
  • Swash plate compressor (wobble plate)
  • Labyrinth piston compressor
  • Swash plate compressor
  • Scroll compressors
  • Free piston machine
  • Diaphragm compressor
  • Side channel compressor

Air compressors specialist dealers & service providers

are e.g. Bauhaus, KAESER, BOGE, PREBENA, Lidl (sells compressors from PARKSIDE, Güde, Einhell), Einhell, RENNER, Güde, HAZET, OBI, Metabo, Danfoss, Frascold, HKT Goeldner, IMPLOTEX, Hornbach, Airpress