The definition of the word circulation conveys the best idea of this mechanism—“The act of moving in a circle, or in a course which brings the moving body to the place where its motion began,” hence, a circulating pump is one which causes the water to flow through a series of pipes or conduits, as for example, the water in a steam boiler as in the Ahrens Fire Engine, see page 126, Fig. 426, or in marine boilers, or forces cooling water through a surface condenser.
A centrifugal pump driven by an independent engine, see page 219, Fig. 497, is generally used for the latter purpose.
Fig. 454A.
The annexed engraving, Fig. 454A, represents a circulating pump attached to a salt water evaporator and distiller for recovering fresh water at sea. The pump at the lower right-hand corner of the engraving takes salt water through the suction at the bottom and passes it upward through the condenser and overboard through the circulation discharge. Any steam pump having a sufficient capacity may be used as a circulating pump.