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.
Thread types: BSPP (G), BSPT(PT), NPT, Metric;
Pressure range marking: PSI, Kg/cm2 ,MPa, Bar;
Pressure range: 0-30PSI-10000PSI;
Case: carbon, stainless steel;
Inlet style: bottom, back;
Mounting style: bottom , back, panel, U bracket;
General dry gauge, liquid filled gauge;
Air Pressure Gauge (PDF)
Wartungseinheit is the nice German word for Air Treatment.