The water of condensation leaves the condenser at the bottom and is drawn off by the vacuum pump. The water from the circulating pump enters at the bottom right-hand end; following the direction indicated by the arrows, it flows through the lower half of the tubes towards the left whence it returns through the upper half of the tubes towards the right and escapes overboard through the water outlet pipe.
It will be observed that the coolest water encounters the lowest temperature of steam at the bottom, hence the best results are reached. There is also a baffle plate just above the upper row of tubes to compel a uniform distribution of exhaust steam among the tubes, as shown in the engraving.
These tubes are usually small—1⁄2″ outside diameter—of brass and coated with tin inside and outside to prevent galvanic action which is liable to attack the brass tubes and cause them to corrode.
Fig. [581] shows an end view of the right-hand head of the surface condenser here described.
Fig. 583.
A single tube is shown in detail in Fig. [580]. One end of the tube is drawn sufficiently thick to chase upon it deep screw threads, while a slot facilitates its removal by a screw-driving tool. The other end is packed and held in place by a screw gland, which is also provided with a slot. In this way the tube is firmly held in one head, and, though tightly fitted in the other, is free to move longitudinally under the influence of expansion or contraction, due to the varying heat.
In some cases engineers prefer the ordinary arrangement of screw glands at both ends of the tubes, with the usual wick packing.
The mechanism illustrated in Figs. [582] and [583] shows a combined condenser and feed-water heater. A compact and efficient method of heating the feed-water from the hot well is of great importance; this is the case in cold weather when the circulating water is at a low temperature.