Circulator pumps, commonly called circulators, are a single stage overhung centrifugal pump designed to provide minimal head to overcome pipe friction losses of the system in which they are installed. Typical applications are hydronic heating or cooling and potable hot water recirculation to provide on-demand hot water.
As illustrated in Image 1, ANSI/HI 14.1-14.2 defines three types of circulators, which are all horizontal in-line pumps but are differentiated by being close-coupled canned motor (CP1), close-coupled (CP2) and flexibly coupled (CP3) types. Circulators look very similar to other overhung in-line pumps defined with ANSI/HI 14.1-14.2 but are differentiated by their horizontal motors and their dedicated purpose design for residential and commercial water circulation.
For more information on circulator pumps, refer to ANSI/HI 14.1-14.2 at pumps.org.