Know-How | Compressed Air Glossary

Many terms used in the compressed air and gas sector are not terribly common outside of the industry and don't find their way into everyday use.  Therefore, as an added value to those who are new to the industry or to our website, please use our searchable glossary of commonly used terms as they relate to compressed air and gas technology.

Glossary Filter
Process of attracting one substance into the mass of another, so that the absorbed substance combines with the absorbent.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Filtration efficiency
Amount of contaminant removed by the filter divided by the amount of contaminant entering the filter, usually expressed as a %.
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.
Organic compound consisting mainly of hydrogen and carbon.
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.
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.
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).
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 condesate represents a real impurity. This one percent can be disposed of relatively easily and inexpensively by the separation of condensate.
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.
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.
Partial pressure
Absolute pressure exerted by any component in a gas mixture.
The equivalent sphere diameter provided by a measuring device.
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 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.
Refrigeration dryer
Dryer liquefying part of the condensable vapours by reducing the temperature using refrigeration processes.
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.
No viable or living organisms
Sweep air
Previously dried air used to carry away moisture from a membrane.
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).