Model FJ-28B is counter-top cabinet model, low-volume air sampler with a 1/4 HP oil-less carbon vane vacuum pump, and a constant air flow regulator for use where a near constant air flow is desirable. The regulator holds a constant pressure drop across an in-line orifice by varying the flow through a bypass valve into the pump. This system allows the pump to work at a minimum head drop at all times by permitting it to run cooler; thus extending its service life. The oil-less pump requires no lubrication to maintain optimal efficiency during its service life. The FJ28B unit may be used in enclosed areas or placed in a weather resistant aluminum cabinet for environmental sampling. The typical operating flow range is 0.35 to 3.5 CFM (10-100 LPM).