The Collaborative International Dictionary of English v.0.48:

Precipitator \Pre*cip"i*ta`tor\, n. [L. praecipitator an
   overthrower.]
   One who precipitates, or urges on with vehemence or rashness.
   --Hammond.
   [1913 Webster]

WordNet (r) 3.0 (2006):

precipitator
    n 1: removes dust particles from gases by electrostatic
         precipitation [syn: precipitator, electrostatic
         precipitator, Cottrell precipitator]