In brief
An air preparation unit treats compressed air upstream of consumers, usually by filtering, regulating and, if required, lubricating it, protecting pneumatic components.
Contents
What is Air preparation unit?
Compressed air from the network contains particles, water and often oil residues. An air preparation unit, frequently mounted directly on the machine, removes these contaminants and sets the appropriate working pressure. This allows valves, cylinders and valve terminals to work more reliably and for longer.
The classic combination consists of filter, pressure regulator and lubricator; filter and regulator are often combined in a filter regulator. The filter separates particles and condensate, which is drained manually, semi-automatically or automatically. Fine and activated carbon filters further improve purity. Lubricators add oil to the air but are no longer needed for many modern components. The unit is often supplemented by a shut-off valve for exhausting the system, a soft-start valve for gradual pressure build-up and a pressure switch. The purity of compressed air is described in classes in accordance with ISO 8573-1.
Full filter bowls, clogged filter elements and defective condensate drains are among the most common faults. A pressure drop downstream of the unit leads to incomplete cylinder strokes and lost cycles. Regular visual inspection of bowls and condensate drains therefore belongs in every maintenance plan for pneumatic machines and systems.
In practice: maintenance and procurement
For a replacement, the series, port size, filter rating, adjustment range and type of condensate drain are needed. Filter elements and bowl seals should be kept in stock as maintenance materials and listed with their part numbers in the maintenance plan.
Synonyms and abbreviations: FRL unit (filter, regulator, lubricator) · compressed air treatment unit · filter regulator · service unit · air service unit
Frequently asked questions
What does an air preparation unit consist of?
Typical components are a filter, a pressure regulator with pressure gauge and, where required, a lubricator. The unit is often extended with a shut-off valve for isolating and exhausting, a soft-start valve for gradual pressure build-up, fine or activated carbon filters, a pressure switch and a distributor block. The modules are assembled into one unit using connecting elements.
Does an air preparation unit need a lubricator?
Many modern pneumatic components are designed for unlubricated compressed air and are lubricated for life. A lubricator is then superfluous. However, once oil has been added, lubrication must generally continue permanently, because the oil washes out the initial lubrication. The specifications of the component manufacturers are decisive.
What information is needed to replace an air preparation unit?
Required are the series and size, connection thread, flow rate, filter rating, adjustment range, type of condensate drain, pressure gauge version and additional modules such as shut-off or soft-start valves. For filter elements and bowls, the spare part numbers from the operating manual are often sufficient. A photo of the entire unit helps with identification.
How often is the filter element of an air preparation unit changed?
Fixed intervals are given in the manufacturer’s specifications but depend heavily on air quality. A differential pressure indicator shows when the filter is clogged. If the pressure downstream of the unit drops noticeably under load or the element becomes discoloured, a change is due.