This page is also available in English - Americas

Change now

Compressed Air Glossary

Learn all the technical terms from the world of compressed air here!



Process of attracting one substance into the mass of another, so that the absorbed substance combines with the absorbent.

Adsorption dryer, HOC

Heat-Of-Compression adsorption dryers can be used wherever oil-free compressed air is produced. The heat generated during the compression process is used for desorption in HOC plants.

Adsoption drying with the EVERDRY HOC series

Activated alumina

Highly porous and granular form of aluminium oxide having preferential adsorptive capacity for moisture from gases, vapours and some liquids.

Activated carbon

Any form of carbon characterised by high adsorptive capacity for gases and vapours.

Learn more about the quality and safe exchange of activated carbon!


Physical process in which the molecules of a gas, vapour or liquid adhere to the surface of a solid.


Suspension in a gaseous medium of solid particles, liquid particles or solid and liquid particles having negligible fall-velocity/settling-velocity.

Ambient temperature

Temperature of the environment surrounding the equipment.

Atmospheric air

In the compressed air technology, the atmospheric air drawn in by compressors is referred to as atmospheric air.


Base load

The base load of a compressed air system is the compressed air consumption which is permanently present in an operation during a certain shift. With an optimal design, it is adopted in modern compressed air systems of compressors that do not need to switch during this time, constantly working at full load and thus in the economic optimum range.

Breathing air

Central compressor stations in hospitals today ensure that sterilized air is available in the treatment rooms. For this purpose, the compressed air must be processed to a very high quality level. Decisive here are the compressed air quality classes 1 defined by the standard ISO 8573-1 for solid particles and residual aerosols and the quality class 4 for the moisture content. In addition, the compressed air must be sterilized. Sterile filtration should, however, be decentralized in order to eliminate any negative influences through the pipeline network.

Learn even more about breathing air on our dedicated page! 

Brownian motion

Random movement of very small particles (below 0.2µm) caused by bombardment of those particles by gas molecules. As a result of this random or spiral movement, the particles describe paths much greater than their actual size and are, therefore, easier to trap.



action of uniting small droplets.


Liquid formed in the compressed air.

Safe and economical condensate drainage with the BEKOMAT


Process of changing a vapour into liquid.


Any solid, liquid, or gas, which adversely affects the system.

Contamination level

Amount of solid, liquid or gaseous contaminant present in the compressed air

Cyclone water seperator

The installation of a cyclone separator after the compressed air outlet of a compressor is useful if it is not possible to separate the condensate separated in the compressor aftercooler by a corresponding installed piping or a compressed air tank.

Is a water separator required? More information here! 


Depth type filtration

Filtration accomplished by flowing a fluid through a filter medium providing a tortuous path to capture the contaminants.


Substance with the ability to remove water from compressed air; for example, silica gel (SiO2) or activated alumina (Al203).


Physical process in which the molecules of a gas, vapour or liquid are removed from the surface of a solid.

Dew point

Temperature at which water vapour begins to condense.

Pressure dew point measurement with METPOINT DPM

Dew point, atmospheric

Dew point at atmospheric pressure

Dew point, pressure

Dew point at the specified pressure

Differential pressure

Difference in value between two pressures occurring simultaneously at different measurement points.


Movement of gas molecules, or small particles, caused by a concentration gradient.

Direct interception

Collection of relatively large particles (1,0 µm and over) on or near the surface of the filter medium. The particles collide with the fibres or structure of the filter medium, without deviating from streamline flow.

Dirt holding capacity

The amount of contaminant a filtration device can hold before reaching an operating limit, e.g. allowable pressure drop.


Device which lowers absolute moisture content of compressed air by reducing water vapour content.

You can find the right drying method for your application here! 



Ratio of the particle concentration removed, i.e. upstream concentration minus downstream concentration, to the upstream particle concentration.


Emulsions occur whenever either compressor condensates or airborne pollutants prevent oil and water from separating. If this is the case, simple gravity separation systems for condensate treatment can no longer be used. Instead, special emulsion splitters are needed.

Emulsions in compressed air condensate? BEKOSPLIT provides a remedy! 

Energy costs

Depending on the runtime of the compressor and energy price, the energy costs represent 70 to 80 percent of the total compressed air production costs.

Do you still have potential for optimisation? Learn more about energy efficiency 

Equivalent rated flow

Equivalent flow conditions through the filter to maintain the same velocity at pressures other than the reference pressure stated by the manufacturer.



Device for the separation of solid, liquid or gaseous contaminants from a fluid stream.

Get to know our range of filters! 

Filtration efficiency

Amount of contaminant removed by the filter divided by the amount of contaminant entering the filter, usually expressed as a %.

Interested? More about filter efficiency 


Gas constant

The gas constant indicates the physical work that performs the molecular unit of mass of the gas under unchanged pressure and a warming by 1 K. This amounts to 287.02 kJ / kg * K.


Heat of adsorption

Heat released when a substance is adsorbed by an adsorbant.


Air that is sucked from the atmosphere always contains water vapor. The amount of water vapor absorbed depends only on the temperature and the available volume. Decisive for this is the partial pressure of the water vapor in the air. If the degree of saturation of the air is reached, it is called air with 100 percent relative humidity.

Reliable measurement of residual moisture - with the pressure dew point meter METPOINT DPM


Organic compound consisting mainly of hydrogen and carbon.

Hydrocarbons in the compressed air? Catalysis technology with BEKOKAT solves the problem!


Idle-speed control

The drive of the compressor continues, but no air is compressed. The compressor partially saves the energy required for compression. When compressed air is required, it switches into the load run without delay. The idle-speed mode reduces the engine timing and thus reduces wear.

Inertial impaction

Capture of particles within a device, as they fail to stay within the streamline flow of the fluid being filtered.



Leakages are leaks in the piping system of the compressed air network. Leakages contribute a major part to the the inefficiency of a compressed air system. For new pipelines, leakages including all connected components should therefore be less than five percent. The causes of leaks are usually poorly maintained. Compressed air hand tools, compressed air controlled production machines.

Find leaks quickly with the METPOINT LKD!


Membrane dryer

Membrane dryers are devices where the compressed air is passed through fine tubes (capillaries). Due to the partial pressure differences between the compressed air and the capillaries surrounded by dry regeneration compressed air, the moisture penetrates the pores.

Drying to measure with our membrane dryers 

Molecular sieve

Natural or synthetic materials whose atoms are arranged in a crystal lattice in such a way that there are a large number of small cavities interconnected by smaller openings or pores of precisely uniform size.



Mixture of hydrocarbons composed of 6 or more carbon atoms (C6).

Residual oil in the compressed air? Here is the solution! 

Oil-water splitting plant

If one considers all the costs of the condensate disposal in any case the use of an oil-water separation device is preferable to the collection and disposal of the condensate by a specialized company. The reason for this is that only about one percent of the resulting amount of condensate represents a real impurity. This one percent can be disposed of relatively easily and inexpensively by the separation of condensate.

Gravity separation of oil and water with the ÖWAMAT!

Operating pressure

The correct operating pressure is important for the performance of compressed air tools and machine tools. So it is e.g. possible that a compressed air tool, which normally shows 100 percent power at 6 bar operating pressure, already has a 20 to 25 bar percent reduction in performance at 1 bar pressure reduction. This can e.g. due to overlong supply lines or too small pipe diameter.

Please use our unit conversion tool for the conversion


Paint-wetting impairment substances (PWIS)

Among substances that interfere with the wetting properties of the silicones are many other substances such as fats and mineral oils. The substances do not lead to errors, but must be seen as a source of risk. This should be checked in advance or excluded in general.

High reject rates in the paint shop? Learn more about this topic here! 

Partial pressure

Absolute pressure exerted by any component in a gas mixture.


The equivalent sphere diameter provided by a measuring device.

Detect particles with the METPOINT MCA

Particle size

Length of the greatest distance between two external boundaries


Amount of contaminant passing through the filter divided by the amount of contaminant entering the filter.

Potential free contact

Potential-free contacts usually switch information and control signals which transmits information to another power supply system or cause an activity. That means, they open or close the control circuit of a third system and are often used for communication between the compressor and higher-level control.

Powder coating

For applying the powder on corresponding surfaces in the powder coating compressed air is also needed. The compressed air used for this purpose should be purificated to a grade 4 dryness grade and to a grade 1 residual oil and particle content. It can happen that the powder-coated surfaces have craters. Often silicone residuals are the reason for it.


Device for removing gross contamination before the fluid enters further processing.

Pressure drop

Difference between the high and low pressure sides of a resistance to flow.

Purge air

Previously dried air used to carry away moisture from a membrane.

Purge flow

Fluid flow designed to remove a contaminant from a filtration or separation device.



Decisive for the exact definition of the air qualities today is the standard ISO 8573-1. It distinguishes between water, particle and oil content of the compressed air. The latter two relate to the atmospheric volume.

You can find out everything about ISO 8573-1 here! 


Refrigeration dryer

Dryer liquefying part of the condensable vapours by reducing the temperature using refrigeration processes.

Discover our range of refrigerant dryers now! 

Regeneration air flow

Purge air flow through the off-line drying media.

Relative humidity

Ratio of the partial pressure of water vapour present to the partial pressure of saturated water vapour at the same temperature, expressed as a %.


Silica gel

Porous and granular form of amorphous silica having preferential adsorptive capacity for moisture from gases, vapours and some liquids.



Gas which is at a temperature below its critical temperature and which therefore can be liquefied by isothermal.



Separating device, which removes bulk water (e.g. cyclone separator).