An FRL is a device that conditions the compressed air supplied to pneumatic equipment. This article explains the roles of air cleaning, pressure reduction, and lubrication, and the points to check when using an FRL.

5.1 What Is an Airline FRL?

An FRL is a combination of a Filter, Regulator, and Lubricator, and is called an Airline Filter Regulator Lubricator in English.

Here, “airline” refers to the piping that carries compressed air. The role of an FRL is to provide the cleanliness, pressure, and lubrication conditions required by equipment that uses air.

Table 5-1 Components of an FRL and Their Main Roles

5.2 Roles of Air Cleaning, Pressure Reduction, and Lubrication

Filter: Removing Contaminants

In addition to dirt contained in the intake air, compressed air may contain contaminants generated by the compressor and piping. Particles produced by corrosion inside the piping can also flow into downstream equipment.

The filter prevents such contaminants from entering the equipment. However, the substances and particle sizes that can be removed depend on the type and performance of the filter.

Also, separating liquid water is different from removing water vapor to dry the air. To achieve the required dryness, the air treatment system must be considered as a whole, including dryers.

Regulator: Setting the Working Pressure

The regulator is a device that reduces the pressure of the supplied compressed air and adjusts it to the pressure required by downstream equipment.

Instead of using the supply pressure of the compressed air as it is, the pressure is set to suit the equipment and application.

Lubricator: Supplying the Required Lubricating Oil

The lubricator supplies oil to pneumatic equipment that requires lubrication, and is used to reduce wear and maintain operating performance.

Oil that has entered the air from the compressor has been affected by heat, moisture, and other factors, and therefore cannot be treated as a substitute for the required lubricating oil.

Whether lubrication is needed should be checked against the requirements of the connected equipment. Since air quality also includes conditions on oil content, it is important to match the conditions required by the equipment rather than lubricating uniformly simply because the device is called an FRL.

5.3 Examples of FRL Use in Research and the Importance of Maintenance

Research on pneumatic positioning systems includes an example in which an FRL is placed between the compressor and the control valves to condition the compressed air supplied to the equipment.

In addition, research on energy saving in compressed air systems points out problems associated with degraded air quality, such as reduced operating speed and valve malfunctions. Filter replacement and periodic inspection of regulators, lubricators, and other components are also listed as maintenance items related to energy saving.

Filters cause pressure loss, and the pressure loss increases as contaminants accumulate. An FRL is not a device that can be installed and forgotten; it requires condition checks and maintenance during operation.

5.4 Checks Based on the Equipment Used

The quality required of compressed air differs depending on the application. CAGI documents also indicate that air treatment equipment should be selected and maintained based on the air quality specified by the equipment manufacturer.

Therefore, when selecting an FRL, check not only the working pressure but also the required air quality and whether lubrication is needed. For filters as well, both the required removal performance and the pressure loss must be considered.

About This Article

References

• “A Real-Time Realization Method for the Pneumatic Positioning System of the Industrial Automated Production Line Using Low-Cost On–Off Valves,” Zhonglin Lin et al.
• “A Review of Energy Overconsumption Reduction Methods in the Utilization Stage in Compressed Air Systems,” Dominik Gryboś and Jacek S. Leszczyński

Sources

• Compressed Air and Gas Institute (CAGI), “Air Compressor Selection & Application: ¼ through 30 HP”
• Compressed Air and Gas Institute (CAGI), “Compressed Air Purity Guide”
• Compressed Air and Gas Institute (CAGI), “Compressed Air & Gas Handbook — Chapter 3: Compressed Air Treatment (Dryers and Filters)”

(Last accessed: October 13, 2026)


*This article was compiled based on the author’s understanding and practical knowledge, with reference to the above literature.