An FRL unit is comprised of a filter (F), regulator (R), and a lubricator (L). They are often used as one unit to ensure clean air in a pneumatic system but can also be used individually. Filters remove water, dirt and other harmful debris from an air system.
It strains the air, traps solid particles (dust, dirt, rust), and separates liquids (water, oil) entrained in the compressed air. Filters are installed in the air line upstream of regulators, lubricators, directional control valves, and air-driven devices such as cylinders and air motors.