FRL units or air treatment unit in German: Wartungseinheiten, are used to clean the compressed air in a pneumatic system. Pneumatic actuators and control valves must wrk with clean filtered air with a low pressure.
AC FRL (AC1000~AC5000)
AC FR+L (AC1010~AC5010)
AW filter regulator (AW1000~AW5000?
AF filter (AF1000~AF5000)
AR regulator (AR1000~AR5000)
AL lubricator (AL1000~AL5000)
Air Prep Unit FRL SMC equivalents (Old Style) (PDF)
Wartungseinheit is the nice German word for Air Treatment.