Model LV-22 is a low volume air sampler consisting of a 1/4 HP oil-less, carbon vane vacuum pump with an air flow regulator for use where a nearly 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 pressure drop at all times by permitting it to run cooler; thus extending its service life.