This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol3", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
The next important detail is the cold supply service, which feeds the apparatus with cold water as fast as any warm water is withdrawn. This is the pipe shown coming from the house cistern to the tank, entering it at the bottom. There are no valves in the pipe (unless a stop cock be inserted to shut off the water when repairs or boiler cleaning are to be undertaken), so that there is open connection between the cistern and tank. It will be noticed (see Fig. 35) that the pipe first descends a little below the tank and then rises up to the bottom. This is done intentionally, to obtain a dip - miscalled a siphon - to prevent heated water working back up the pipe into the cold cistern. Hot water will travel, circulate in fact, up a single pipe, but by starting the pipe in a downward direction (where it leaves the source of hot water) this fault is quite avoided. A 6-inch dip is sufficient for this purpose.
On the cold supply connection, and inside the tank, a tee-peice will be observed. The purpose of this is to prevent the inflowing cold water "boring" its way up into the stratum of heated water above. The tee causes the delivery to be in a horizontal direction. An elbow answers the purpose just as well. Occasionally a fitter will make his connection as shown in Fig. 40, this giving a horizontal delivery, but probably the best method is as in Fig. 41, though it is seldom practised. As will be understood, the idea is to deliver the cold water in such a manner as will keep it as a level stratum in the lower part of the tank, not disturbing nor mingling with the heated water above.
From the top of the tank there extends a tube, known as the expansion pipe (see Fig. 35). Water expands to a known degree when heated, and in an apparatus of this kind the greatest amount of expansion is probably about 1 in 28 ) ; that is, 28 gallons of cold water occupy the space of 29 gallons when very hot. The expansion pipe does not accommodate this extra water, however, - for it would have to be a very large pipe to do so in some cases, - but it admits of the water standing at a higher level in it than the level of the water in the cold cistern. The expanded water goes mostly back into the cold cistern each time the range fire is lighted in the morning, while the difference in gravity of the hot and cold waters causes the former to reach a level of from 1 to 2 feet higher in the expansion pipe than the cold-water level in the cistern. Notwithstanding this explanation, the chief purpose served by the expansion pipe is that of admitting of the free escape of air from the apparatus. The filling could not be properly done, or at all, if the tank had no opening in its top ; and if a temporary opening were made, to admit of filling, the air given off by the water when heated afterwards could have no opportunity to escape. It is sufficient if this pipe is carried 2 feet above the cold-water level in installations of medium height, and 3 feet where the apparatus extends up, say, 60 feet.
All draw-off services are branched from the flow-pipe, and, as previously stated, every effort should be made to have this pass as near as possible to the points where taps are to be. It is too often the case that a position is located for the tank, and the pipes then run by the nearest route to it without regard to the points which the taps are to occupy. This commonly means branches of unnecessary length, with the subsequent annoyance of having to run off a good volume of cold water before the tap yields any that is hot. This is not a great fault at a bath, as most makers of good baths recommend that some cold water should be run in before the hot water is turned on ; but at lavatory basins, usually having small taps, the annoyance seldom fails to bring complaints. This trouble can be reduced to some extent by using pipes (for branches) of a less size than the nominal measurement of the tap. Thus a 1/2-inch pipe can be put to serve a 3/4-inch tap, and this it will do quite well, as few 3/4 inch cocks have a bore or way through them equal to the area of a 1/2-inch tube. It is to be strongly recommended that the flow-pipe be run conveniently for the taps, as there is no satisfactory way of making branch circulations with this system of apparatus.
In regard to proportioning the parts of this form of apparatus, the following table will be found satisfactory. From the large number of failures that have been noticed, no hesitation need be felt in saying that by far the majority of them are due to a disproportion of parts. Sometimes the sizes of pipes are at fault, but usually it is the boiler and tank that do not agree. It is always one way, the tank too large for the boiler. There is no widely known rule for calculating the working capacity of range boilers (as there is with heating boilers), and, as yet, there is a marked tendency to overestimate the bulk of water they may be set to work with.
Number of Taps, including
Shape of Boiler.
Width of Fire.
Capacity of Tank.
Square, with arched flue .
Square, A. F. .
F. boot .
3 or 4
Square, A. F. .
3 or 4
F. boot .
Square, A. F. .
F. boot .
5 or 6
The cold-supply pipe should be 1 inch in all cases, except with the smallest works, when it may be 3/4 inch. Expansion pipes should be the same size as circulating pipes. Draw-off branches can be: lavatory basins 1/2 inch, sinks 3/4 inch, baths 1 inch.