Air preparation units (FRL)
Air treatment units (FRL) – general information
FRL – preparation of air as a working medium in pneumatics.
Atmospheric air is polluted with gases, vapour, particles of various chemical compounds but also with dust of various shapes, structure and density usually swirling in the air. The composition and concentration of pollutants in the atmospheric air depends on the location and time of the year. All of these pollutants enter pneumatic systems enriched with impurities brought in during compression, unless they are removed from the air before and after the compression. In pneumatics, compressed air is prepared in special devices (air preparation units – FRL) which:
- remove impurities from air (F-filter),
- regulate pressure to the required level (R-regulator),
- lubricate the air (L-lubricator).
In addition, a shut-off start-up valve is usually installed before FRL units whereas a soft-start valve after FRL units (before a final device).
Filtered air should not contain:
- water in the form of drops – water vapours are allowable as long as the dew-point (the condensation temperature of the air at a given pressure and humidity) is about 5 ÷ 10°C below the lowest temperature in the installation, and the relative humidity at the lowest working temperature does not exceed 80% (relative humidity is expressed in %, 0-dry air without water vapour, 100% saturated with water vapour – its cooling causes immediate condensation),
- oil and other fluids in the form of drops,
- mechanical pollution greater than 50 µm
List of products:
FRL units
Filters
Regulators
Lubricators
Filter-regulators
Shut-off and soft star valves
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FAQ – Air preparation units
The abbreviation FRL stands for a compressed air preparation unit consisting of:
F – filter – removes contaminating particles and moisture (condensate) from a compressed air system;
R – regulator – reduces and maintains pressure at a required level;
L – lubricator – injects a lubricant (oil) into an application that requires lubrication.
The condition of a filter element should be verified based on the quality of the compressed air. The contaminated (dirty) filter element can cause pressure, flow and performance drop. The filter element should be replaced every six months according to the manufacturer’s recommendations to ensure the correct operation of the pneumatic system.
Depending on the application, compressed air filters are equipped with filter elements of different gradations.
A filtration level, expressed in micrometres (µm), determines the size of particles above which the particles are retained by the filter.
The most common levels of filtration:
Pre-filtration (coarse) – 5µm or 20µm filter element
Fine filtration – 0.01 µm filter element
A lubricator is recommended for:
– operation in a damp and dusty environment,
– operation of actuators at speeds > 1 m/s,
– valve switching frequency > 3 Hz.
When selecting a pressure reducing valve, apart from the supply pressure and operating temperature, it is necessary to take into account the required flow rate which is related to the size of a connection. Whereas the control range should be matched to the required operating pressure (a pressure reducing valve maintains the set value more accurately and has a smaller hysteresis).