It is service unit used in Pneumatic system which is combination of three devices named as Filter, Regulator and Lubricator.
 
Function of FRL unit:
Filter – To remove the micron and sub-micron particles present in the entering air of compressor. It is used to separate out contaminants like dust, dirt particles from the compressed air.
 
Regulator – In pneumatic system the pressure of compressed air may not stable due to possibility of line fluctuation. Hence there is a need to maintain and regulate the air pressure. This function is performing by regulator.
 
Lubricator – Sliding components like spool, a pneumatic cylinder has sliding motion between parts. It may cause friction and wear and tear at mating parts. To reduce friction, lubricating oil particles are added in the compressed air with the help of lubricator.