Conventional cascade impactors have been used extensively for fractionating airborne particles according to their aerodynamic sizes, enabling the size distribution to be determined by analyzing the collected particles.  This technique has sometimes created problems, including stage overloading and particle re-entrainment.

The Virtual Impactor does not collect particles, but merely redirects them into two different air streams according to the cutoff characteristics.  The same principle of inertial separation is used, but the impaction plate is replaced by a region of relatively stagnant air contained in the cavity of a receiving probe.  The fine  particles follow the streamlines of the major air flow, while the coarse particles pass into the forward minor flow region.  Both particle size groups can, subsequently, be ducted for any desired methods of analysis or collection.  This instrument is generally free from particle bounce and re-entrainment  that often occurs in other size separating samplers.

Stock # 02-300  Virtual Impactor

Stock # 02-301  Virtual Impactor Control Unit