_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.
[Illustration: 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._