The condenser is an oblong or circular box of cast iron fitted in one
of two ways, either with the tubes horizontal or vertical; at each end
are fixed the tube plates, generally made of brass, and the tubes pass
through the plates as well as through a supporting plate in the middle
of the condenser. Each end of the condenser is fitted with doors for
the purpose of enabling the tube ends to be examined, drawn, or packed,
as may be necessary. The tube ends are packed in various ways, and the
tubes are made of brass, so as to resist the action of the water. The
water is generally sucked through the tubes by the circulating pump,
and the steam is condensed by coming in contact with the external
surface of the tubes. In some cases the water is applied to the
external surface, and the steam exhausted through the tubes; but this
practice is now generally given up in modern surface condensers. The
packing round the tube ends keeps them quite tight, and in the event
of a split tube, a wooden plug is put in each end until an opportunity
offers for drawing it and replacing with a new one.
The condenser may be made of any convenient shape. It sometimes forms
part of the casting supporting the cylinders of vertical engines; it
is also frequently made cylindrical with flat ends, as in fig. 25. The
ends form the tube plates to which the tubes are secured. The tubes
are, of course, open at the ends, and a space is left between the tube
plate and the outer covers, shown at each end of the condenser, to
allow of the circulation of water as shown by the arrows.